We are born with miraculously integrated bodies and minds. Our lungs draw in vital oxygen, essential for producing energy. Our hearts ceaselessly pump blood through vast networks of vessels to all of our tissues and organs. Raw materials are transformed into fuel by our digestive systems. Our muscles and bones propel us through the world, allowing us first to stand, then walk, then play and work.

Each day our brains take in a barrage of new information, filtering it, selectively storing it, and adapting their way of working accordingly. At the end of each day, we recharge and reset our systems by sleeping. All of us come equipped with a self-contained set of tools that, properly used, may allow us to live 100 years, or maybe even longer.

Beginning early in our lives, though, our genes, our environment, our culture, and our own free will conspire to test this marvelous organism—sometimes to the breaking point. There are people who maintain their health and live long, fruitful lives, sustaining minimal wear and tear. But others—perhaps most of us—push our bodies to the limit. Instead of eating the way our bodies were designed to eat, we indulge in foods filled with sugars and other refined carbohydrates, trans fats, and unhealthy food additives. Instead of walking to nearby destinations, we drive our cars. We sit most of the day. Some of us smoke. Some of us drink too much. Many of us allow negative feelings and stress to rule our thoughts. Not many of us get adequate sleep. The wrong choices trap us in a lifestyle that actually endangers our lives.

The effects of these poor choices compromise every system that keeps us well, and the damage is not pretty. After years of a diet high in refined carbohydrates, arteries become narrow and clogged with plaque, raising the risk of cardiovascular disease and heart attack. We find ourselves on the unhealthy path to metabolic syndrome, type 2 diabetes, osteoarthritis, and cancer. Eating too much of the wrong foods and getting too little exercise allows fat to build up around our organs and beneath our skin. Smoking fills our lungs with toxins, damaging our health in myriad ways. Not getting enough sleep worsens our memories and disrupts an important hormone cycle that prevents us from overeating. And too much stress compromises our body's natural immune system, the very tool that would help us combat much of the other damage.

Return to the Path of Good Health

Fortunately, we have the ability to choose.

That’s where our series of HealthJournals on Wellness come in. Our Wellness series will show you how to completely change your lifestyle to a healthy and sustainable one that will restore your vitality and reverse chronic medical conditions. It will provide you with innumerable health benefits. It will lessen dangerous abdominal fat, lower chronic inflammation, and reduce the threat of other chronic diseases. Your risk of getting heart disease, cancer, diabetes, and autoimmune diseases will be greatly reduced. You will be likely to live longer, too. What’s more, your systems and organs will be provided with all the nutrients they require, so that your hunger will be satisfied, and your body brought into homeostatic balance.

This wellness information is based on real science that refutes current mainstream medical notions of what we should be eating. In this series, we explain the most natural way to eat—so that fat melts away and the body’s hormonal systems rebalance themselves. In doing so, we turn popular notions of a “healthy diet” on their head. Moreover, we give you all the leading science on other aspects of wellness in your life—including how to break your bad habits, the benefits of sleep, how to de-stress, and the real benefits of exercising.

It’s rarely too late to make changes that can reverse damage to your abused organs and tissues. Even people who are sensitive to carbohydrates, and therefore genetically predisposed to putting on weight, can get back on the path to good health. By eating the right foods, exercising, modifying your negative habits, quitting smoking, sleeping well, and celebrating life, you can reverse many chronic conditions—and increase your enjoyment of life immeasurably.

We hope that you will continue to explore the miracle that is your body, knowing that the good choices you are making will enable you to enjoy a life full of activity and fulfillment. You have the power to keep your body and mind healthy, strong, and alive. You can live longer and live better.

To life!

Wellness and The Science of Fat

Understand why the advice that many experts have been giving us for the last 40 years is just plain wrong. You’ll see how your body uses different nutrients and exactly why refined carbs force your body to store fat—but make it impossible to burn it off.

­Fat, or adipose tissue, is found in several places in your body. It's usually found underneath your skin (termed subcutaneous fat) or inside your abdomen (called visceral fat). In obese people, the fat storage system can go haywire, and excess fat can start to accumulate in other tissues as well. This type of fat is known as ectopic fat.

Subcutaneous fat is the kind that lies just under your skin. You can pinch it between your fingers. Most people don’t like having too much of it for aesthetic reasons, but it’s not as dangerous to your health as visceral fat. Subcutaneous fat can be a warning sign: If you carry a lot of subcutaneous fat on your belly, it’s a pretty good bet you have an overabundance of visceral fat as well.

Visceral fat, on the other hand, is found deep inside your abdomen, surrounding your vital organs and in your liver. When normal processes in your body are thrown out of whack and weight gain occurs, you are likely to accumulate those extra pounds in the form of visceral fat. Excess amounts of visceral fat are dangerous for your health because visceral fat secretes toxic chemicals that travel directly into your liver and then into your bloodstream. Having too much visceral fat leads to developing a whole slew of adverse health conditions, including metabolic syndrome, hypertension (high blood pressure), type 2 diabetes, and heart disease.

IMAGE: Visceral fat is found deep inside your abdomen, surrounding your vital organs. It's different from subcutaneous fat, which lies just underneath your skin.

Ectopic Fat

Your fat cells are generated when you're just a developing fetus and again when you enter puberty, but normally none are generated after that. When you store more fat (gain weight), your fat cells increase in size, but not in number. Fat accumulation is usually a slow process, and your fat cells can expand up to 20 times in diameter, storing much of the excess fat from your bloodstream. However, at a certain point the fat cells become too full and are unable to take up any more free fatty acids. Because they can no longer store fatty acids, they start releasing them back into the bloodstream. These excess fatty acids start to accumulate in other tissues and organs that really aren’t designed to store excess fats, such as the liver, heart, skeletal muscle tissue, and even the beta cells of the pancreas (the cells of the pancreas that secrete insulin). This wayward fat is known as ectopic fat, and it is believed to interfere with normal metabolism and lead to an increase in insulin resistance.

How Fat Changes Over Time

Exactly where fat is concentrated in your body, and how much, depends partly upon whether you're a man or woman as well as what stage of your life you're in. Women and men tend to store fat in different places, and normal hormonal changes during certain life stages can influence fat accumulation. Men tend to carry weight on their chest, abdomens, and buttocks—they’re “apples.” Women, on the other hand, tend to carry fat on their breasts, hips, waists, thighs, and buttocks, making them “pears.” This general difference in fat distribution between men and women is initially determined by the hormones estrogen and testosterone during puberty.

Girls entering puberty have only slightly more fat than boys entering puberty, but girls finish with 50% more fat. Although girls enter puberty with an average of 15% body fat, fat comprises about 28% of body weight as they enter adulthood. (To maintain regular ovulatory cycles, it’s necessary for girls and women to have about 25% body fat, which explains the large post-puberty increase.)

When women reach menopause, they tend to gain excess fat on their midriffs as well as in the typical "pear" locations. Belly fat accumulates after the onset of menopause because levels of the hormone estrogen decrease at that time. Estrogen can suppress the activities of an enzyme called lipoprotein lipase (LPL). As you'll see, LPL plays an important role in weight gain. LPL sits on the outside of your fat and muscle cells. On your fat cells, LPL directs the cells to take in fat. At menopause, more LPL is present on the fat cells of the midriff and less estrogen is present to suppress its activities. This results in additional fat being pulled into those fat cells for storage.

IMAGE:Female fat distribution during puberty (left image), adulthood (middle image), and menopause (right image)

During puberty, boys actually lose fat and gain muscle mass. Most men can maintain a reasonably stable weight early in their adulthood, but after about 50 years of age, more fat tends to accumulate just above the waist. As men age, they secrete less testosterone. Testosterone, like estrogen, has the ability to suppress LPL, which pulls fat from the bloodstream into fat cells. For men, LPL activity is high in the fat tissue of the gut. When men are no longer able to suppress the LPL as effectively, they tend to gain weight.

IMAGE:Male fat distribution during puberty (left image), adulthood (middle image), and in old age (right image)

Besides estrogen and testosterone, a number of hormones (including insulin) as well as other factors influence fat regulation and distribution. People come in all shapes and sizes. Everyone puts on weight differently, and at different rates. Some people don't gain excess fat at all! There are many factors involved in each individual’s susceptibility to weight gain. But first, let's explore why we store fat in the first place.

Fat performs many functions in your body: It provides energy, produces hormones, cushions and protects your organs, provides padding under your skin, and helps to regulate heat in your body. Its main job, however, is to store energy in the form of triglycerides.

Fats are your major form of stored energy. They are very efficient in this regard: A single gram of fat stores 9 kcal of energy, about twice as much energy as a gram of carbohydrate or protein. Such a concentrated form of stored energy means there’s less bulk to carry around, and it also enables us to survive for long periods of time without eating. A normal body is about 20% fat. That’s enough stored fuel to enable someone to go without food for 20-30 days!

IMAGE: A microscopic image of fat cells (main image) and a close up of an individual fat cell (callout)

If you look at a fat cell under a microscope, it looks as though it’s almost empty. In fact, most of the space in the cell is taken up by lipids (fats), which push other parts of the cell (like the nucleus and cytoplasm) to the cell’s edges. The large lipid content of the cell makes it a good cushion against impact, helping to protect the body’s organs. And because lipids are very poor conductors of heat, fat tissue is an excellent insulator. Here's some more information on the roles that fat plays in your body:

Fat Provides Energy

Most of your body fat is stored in fat cells called adipocytes. When you eat carbohydrates, protein, or fats in excess, any extra nutrients that are not used immediately for energy are converted to triglycerides and stored in adipocytes for future use. Mitochondria, the tiny “powerhouses” inside your cells, have the critical function of converting stored triglycerides into energy so that your body can do its work.

Fat Builds Hormones

Fat actively secretes a number of hormones your body needs. These include prostaglandins, which regulate many of the body’s functions, and sex hormones, such as estrogen.

Aromatase, a hormone produced by fat tissue, is necessary for the production of estradiol. Estradiol is the major form of estrogen in humans. It has a major impact on reproductive and sexual functioning, most importantly in women but also in men. Estradiol affects several organs as well as your bones. When you have excess fat, you produce more estradiol than is normal. This can affect your sexual and reproductive functions. It can also increase your risk of cancers that are sensitive to estrogen, like uterine and breast cancers

Another hormone produced by fat tissue is adiponectin. Adiponectin assists insulin in maintaining blood sugar levels in a healthy range. However, if you become overweight, adiponectin production slows or shuts down altogether. Adiponectin stops helping insulin, increasing the likelihood that you will become insulin resistant and develop type 2 diabetes and heart disease.

Many other hormones are produced by fat tissue, and many other things can go wrong in your body if too much fat tissue is present. The examples above are just two of many that show the importance of hormone production in fat tissue.

Fat Makes Up Your Brain

Fat is an important component of your brain—in fact, more than 50% of the dry weight of the brain is fat. Your brain and nerves would not work without fat. Structural fat is found in the myelin sheaths of neurons and is a key component of the synapses, or connections, between them. Myelin speeds the transmission of nerve impulses.

Fat Surrounds Your Cells

Your body is made up entirely of cells, and cells are wrapped in membranes that enclose their contents. Cell membranes keep the contents of the cells separate from the watery environment around them, selectively allowing nutrients and waste products to pass in and out as needed. Fats and lipids are crucial components of cell membranes.

Fat Insulates Your Body and Protects Your Organs

Subcutaneous fat, found directly below your skin, is an efficient insulator. It helps your body retain heat and maintain a constant internal temperature: 98.6° F (37.0° C). Fat provides cushioning around internal organs and protects them from injury.

Fat Contributes to Your Immune System

Fat cells are also important contributors to your immune system, which helps fight off sickness and heal injured tissues. Among many other substances, fat cells manufacture cytokines, signaling proteins that affect cell behavior. Types of cytokines include interleukins, tumor necrosis factor, and interferons, which trigger inflammation and respond to infections.

We’re programmed to store fat because in the right amounts, it's crucial to the proper functioning of the body. But why are some people seemingly predisposed to put on extra fat, while others stay lean?

Many factors are at work in people’s differing tendencies to gain weight. Genetics do play a part, but lifestyle choices and environmental factors are also strong influences. The good news is that your genetic makeup only increases the likelihood that you’ll gain weight—it doesn’t determine whether or not you become overweight or obese. Even if you're predisposed to gain weight, you can decrease the risk through diet and exercise, as well as by altering unhealthy habits.

You've already seen, throughout this book, many of the unhealthy habits that can send your system out of balance, setting you up for weight gain and its accompanying ills. Indulging in bad habits, not sleeping enough, and being constantly stressed take their toll. By far the biggest factor, though, is the food you eat. Eating the right foods is the only way to keep weight gain at bay—especially if your genetic makeup makes you more sensitive to sugar or susceptible to insulin resistance.

Your body needs energy to power your muscles, fuel trillions of cells, and drive the innumerable biological reactions that take place throughout your system every day. This energy comes from the food you consume in your diet. To better understand what happens to the food you eat, and what determines whether it's used for fuel or stored as fat, let’s take a look at what happens when you eat a typical meal.

When you eat a meal, it's likely to contain a mixture of carbohydrates and fat. In order to keep your blood glucose levels in check, your body must first deal with the carbs you’ve eaten. All other nutrients are ignored until this happens. Therefore, any fat that was a part of the meal will be shipped off immediately to be stored, without being used for fuel, while your body deals with the carbs.

The carbohydrates are broken down into glucose in your digestive system and released into your bloodstream. Your body will then try to clear the glucose from your bloodstream. This can happen in three different ways:

1. The glucose may be taken up and burned for fuel by cells in your body (at insulin's prompting). The more glucose in your blood, the more insulin will be present to make sure this gets done. This is why many refer to glucose as the body's preferred fuel source. This is technically incorrect, as glucose isn't actually preferred. Rather, it must be used first because high levels of glucose in the blood are dangerous.
2. If space is available, some of the glucose may be stored as glycogen in your muscle and liver cells. Glycogen is the storage form of glucose. Remember, there is limited space for glycogen stores. Glycogen stores in muscle tissue are used by muscles as their own individual sources of quick energy.
3. Any glucose that is left over after fuel demands have been met and glycogen stores have been replenished will be converted into fatty acids, then stored as triglycerides (fat) in your fat cells.

In essence, your body uses what it can of the glucose, and the rest is stored as fat.

Say it’s been a while since your last meal. Your body has been burning and storing the glucose derived from the foods you’ve eaten. Your blood sugar levels have decreased, and your insulin levels have gone down as well.

The glucose has been used up, but your body still needs fuel. Now, fatty acids take up the role of fuel source. Because insulin is not present, the fat stored in your fat cells can be broken down into fatty acids, released back into your bloodstream, and burned as fuel. (Remember, fat can only be released from storage when insulin is not present.) Your body’s use of fatty acids as a fuel source is a normal, daily occurrence—it’s the reason you can sleep through the night without eating or starving!

When your body is functioning normally and you're maintaining a healthy weight, the fat you're storing immediately after meals (derived from both the carbs and the fat you eat) is balanced out by the fat you're burning in-between meals or at night when you're sleeping. This is the ideal scenario!

Problems arise, however, when your glucose and insulin levels remain elevated. Imagine now that you are constantly eating meals and snacks high in both carbs and fats throughout the day, as is the case in a typical American diet. This results in constantly high blood glucose and insulin levels throughout the day. As before, the fat from each meal or snack is immediately stored as your body’s first priority is to get your blood glucose levels down. This means that insulin must be released into your bloodstream. Some of the glucose is used for fuel, some is stored as glycogen. But when you eat large amounts of carbohydrates, only so much of it can be used as fuel or stored as glycogen. The remainder must be converted to fat and stored.

Here’s the crux of the matter: When your glucose levels remain high, your insulin levels must remain high, too. And when insulin levels are high, all that stored fat can’t be released from your fat cells and burned for fuel. It’s trapped!

You can see, then, that constantly elevated levels of insulin are really the problem. Insulin, when present, will always ensure that fat gets stored—and that it stays there! This occurs through the action of insulin on the enzyme lipoprotein lipase (LPL), which you learned about earlier. Insulin is the primary regulator of LPL. LPL sits on the outside of your fat cells and pulls fat from the bloodstream into the fat cell. Insulin activates LPL on the fat cell: The more insulin you secrete, the more active the LPL on the fat cell, and the more fat is pulled into that fat cell to be stored.

LPL can also be found on your muscle cells. There, LPL still pulls in fatty acids from your bloodstream, but in this case it's good because the muscle cell can't store fat, but will burn the fatty acid for fuel. Unfortunately, insulin suppresses the LPL found on your muscle cells.

The upshot is that insulin encourages the storage of fat in your fat cells while it discourages the burning of fat in your muscle cells!

But it doesn’t end there. Insulin has another role: It suppresses an enzyme called hormone-sensitive lipase (HSL). HSL is found inside fat cells, where it helps to break down stored triglycerides into fatty acids. Triglycerides are too large to exit fat cells, so they must be broken down into their smaller components, fatty acids. Fatty acids are small enough to exit the cell. Fatty acids that are able to escape from fat cells can be burned for fuel. When the presence of insulin suppresses HSL, however, the triglycerides remain trapped in your fat cells, unable to exit and unusable as fuel.

To add insult to injury, insulin can also cause you to overeat and crave even more carbohydrates. After a carb-rich meal,large amounts of insulin are circulating in your bloodstream, ordering cells to take up glucose. The insulin causes your blood sugar level to go down quickly. Your insulin levels, though, have not yet had time to decrease, so fat is still trapped in your fat cells. The fast drop in your blood sugar (plus not having another fuel source available) makes your body think you’re starving—even though you have all those fat stores to burn off. This sends you looking for more food, often in the form of another refined carb. You specifically crave carbs because they are the only macronutrient your body can burn when insulin is present.

This can lead to a vicious cycle. Your fat cells store more and more fat, while at the same time you feel hungry and crave still more carbs. With constantly high levels of insulin inhibiting fat breakdown, fat cells continue to grow. That’s how body fat piles on.

In the end, it's insulin's job to increase the fat we store and decrease the amount that we burn. When insulin levels are high, you store fat. When insulin levels go down, fat can be freed from your fat cells and be used for fuel. When everything is balanced, as we saw in the first example, insulin's role in fat storage is not a problem. However, if insulin levels are constantly elevated or extra amounts of insulin are being released into your bloodstream—which is what happens when you eat refined carbs throughout the day—your body spends more time storing fat than burning it.

You may be wondering why some skinny people eat a lot of refined carbs and never seem to put on a pound. Obviously, they secrete insulin too! So why aren't they gaining weight? That's where genetics come in.

We, as humans, tend to crave carbohydrates, and there’s a good reason for that: Carbs break down quickly and easily and provide us with fast energy. Our species has been evolving for a couple of million years, and for the vast majority of that time we were hunter-gatherers. We became farmers and herders only about 10,000 years ago. Ten thousand years is the blink of an eye in evolutionary terms.

According to one theory, our bodies are still adapted to a hunter-gatherer diet, in which refined carbohydrates and pure starches are quite rare. Our ancestors may have raided the odd bee hive, but for the most part their diet included very few grains (a major source of carbs), and the fruits and vegetables that they could only eat seasonally, were more fibrous and less sweet than our modern, hybridized versions. Our ancestors didn’t have corn, potatoes, beans, cultivated grains like wheat and rice, or sugar. The bulk of their diet consisted of meat and fish, nuts, seeds, and fibrous fruits, roots, and vegetables. About 72% of the food we eat today was unavailable 10,000 years ago! That’s why, according to this theory, our systems are unsuited to process the large quantities of carbohydrates we typically consume today.

We still have cavemen physiologies, but we eat modern high-carb diets and live sedentary lives. The result is a health train wreck. We consume refined carbohydrates all day long, and our bodies simply aren’t equipped to handle that kind of sugar onslaught.

Certain individuals, though, do better on a carb-heavy diet than others. Although we may not be genetically designed to handle the modern high-carb diet, we all inherit genetic traits that determine whether the carbs we eat are more likely to be turned into energy or stored as fat. While we're not far off genetically from our hunter-gatherer ancestors, some lucky people still seem to have a leg up when it comes to how the insulin in their bodies responds to the carbohydrates in their diets.

Genetic Influence on Insulin and Glucose Sensitivity

There are many reasons why you might be more likely to store fat than to burn it or vice versa. Most of it has to do with how your body is programmed genetically to respond to carbohydrates.

How much insulin you secrete in response to ingested carbohydrates (which turn into blood glucose) can influence the balance between fat storage and fat burning. Two people could eat exactly the same meal, with exactly the same amount of carbohydrates, and the resulting insulin response could be different for both. One person may secrete very little insulin. Less insulin means less fat storage. The other person, conversely, might be much more sensitive to glucose and therefore secrete a lot more insulin. This person is geared toward fat storage and will tend to put on more weight. To make matters worse, the individual who secretes more insulin is more likely to have cells that are, or will become, more resistant to the effects of insulin.

This brings us to the next important genetic factor that determines weight gain: the sensitivity (or resistance) of the cells in your body to insulin. Some people have cells that are naturally resistant to insulin. Other people may develop insulin resistance over time. Generally speaking, the more insulin you secrete in response to carbs, the more likely it is that you will become insulin resistant.

When cells are resistant to insulin, it means that they don't react when insulin signals them to take up glucose from the bloodstream. This causes the pancreas to secrete even more insulin, because increased levels of insulin can force the cells to accept glucose—for a while. Over time, the cells become increasingly insulin resistant, and even high levels of insulin can’t get them to admit glucose. Higher levels of insulin also lead to more fat storage.

Genetic differences in people’s sensitivity (or resistance) to insulin extends to different types of cells as well. In people who are genetically predisposed to weight gain, insulin resistance generally occurs in the muscle cells. Muscles are the main users of glucose in the body. When they don’t take up glucose because they are insulin resistant, much less glucose is burned for energy, and more remains in the bloodstream. On the other hand, in those people predisposed to weight gain, fat cells tend to stay fairly sensitive to insulin. When their muscle cells won't take up the glucose, the fat cells take it up instead and store it as fat.

People at the other end of the spectrum, who are far less susceptible to accumulating fat, tend to have the opposite form of resistance. Their muscle cells are very sensitive to the effects of insulin and take up glucose readily, so that much of their blood glucose is burned for fuel. At the same time, their fat cells tend to be more resistant to insulin, meaning less fat is stored.

Everyone is different. Your genetic material—your DNA—determines many things about you, including your body’s response to carbohydrates. If you eat the typical American diet and you seem to pack on the pounds easily, you can almost assume that you are sensitive to carbohydrates for one or all of the reasons discussed above. This, unfortunately, is not something that you can change—but it’s something you can control. Now you’re armed with the knowledge of how to keep your insulin levels in line.

The FTO Gene

Researchers have discovered a gene that could contribute to weight gain in some individuals. This gene doesn’t seem to be related to a person's genetic sensitivity to insulin. It is named the FTO gene, sometimes referred to as the "obesity gene,” and it’s located on chromosome 16. A gene is a distinct portion of a cell’s DNA. Chromosomes consist of bundled genes. Humans have 23 pairs of chromosomes, which are found in every cell of the body. All together, the 23 pairs of chromosomes contain all the genes that give you your individual traits.

People who have one copy of the FTO gene (that is, it’s found on only one of the paired chromosomes) weigh 4.5 pounds (2 kilograms) more, on average, than people who do not have it. Those who have two copies of FTO (in other words, it’s found on both of the paired chromosomes) weigh about 9 pounds (4 kilograms) more.

It’s important to remember that even though FTO is referred to as the "obesity gene,” it isn’t deterministic. Someone who has the FTO gene variation won’t necessarily become obese. Many other factors, including lifestyle, diet, and other genes, are also involved.

While it isn't clear exactly how having the FTO gene contributes to weight gain, it has been found that the FTO gene is widely expressed or “turned on” in the hypothalamus, a part of the brain that controls our appetite. FTO is also expressed in the areas of the pancreas where insulin is produced.

IMAGE: Chromosomes inside of a cell that is about to divide (left image). Region 16Q12.2 (highlighted in right image) is the FTO gene's location on chromosome 16.

Genetic Disorders and Other Diseases

Certain genetic diseases and disorders can cause some people to be more sensitive or less sensitive to glucose. Diseases of the pancreas, such as type 1 diabetes, pancreatitis, and pancreatic cancer, can affect the ability of the pancreas to produce insulin. Other diseases and genetic disorders may affect an individual’s ability to metabolize sugar as well. These disorders include hyperthyroidism, Cushing syndrome, acromegaly, Down syndrome, Klinefelter syndrome, and Turner syndrome.

Your genetic inheritance plays a role in determining how susceptible you are to packing on the pounds, but it's the environmental factors—the things that you can often change—that are the major influences of whether or not you become obese. The most important of these factors is the food you eat. There are, however, many other environmental factors that can contribute to weight gain. For example, it may be hazardous to walk or exercise in certain neighborhoods due to crime or a lack of pedestrian-safe areas. There might not be access to fresh food in the area. Some people may not be able to afford fresh produce and other unprocessed foods.

Cultural habits can play a part as well. In the Southern US, for instance, many foods (including vegetables) are normally deep fried and consumed along with plenty of refined carbs—a recipe for a health disaster! Families are a major influence. Members of a family generally have about the same eating habits and level of activity. If one or both of your parents are obese, you are more likely to be obese as well. People are also more likely to become obese if their friends are obese.

As you saw earlier, chronic stress and not getting enough sleep may cause you to pile on the fat. Sleep deprivation can make you hungrier because it unbalances the hormones that regulate hunger: leptin and ghrelin. Some researchers theorize that overeating may result from reduced impulse control, a consequence of sleep deprivation.

When you’re chronically stressed, constantly high levels of cortisol make you less sensitive to leptin (which signals your brain that you are full), causing you to overeat. A third hormone, neuropeptide Y (NPY), is one of the most abundant appetite-related neuropeptides in the brain and is an extremely potent appetite stimulator. NPY increases fat storage by enhancing the triglyceride-forming activity of lipoprotein lipase (LPL). Studies show that high refined-carb intake increases NPY activity in the brain’s hypothalamus.

In many cases, making simple changes in your lifestyle—getting more sleep, relaxing, and removing refined carbs from your diet—may be all that's standing between the old, overweight you and the new, healthy you.

While getting enough sleep and keeping stress under control are important in controlling weight gain, it should be clear by now that the best way to direct how much fat you're storing or burning is to control insulin, whether or not you're genetically predisposed to gaining weight. The only way to keep your insulin levels low is to limit your carbohydrate intake.

Eat fewer carbs, and make the carbs that you do eat nutritious, low GL, and high in fiber, so they don’t spike your blood sugar or insulin. Because your insulin levels remain low, there is ultimately less fat storage and more fat burning.

When you eat a ketogenic or low-carb diet, your body doesn’t have to deal with so many incoming carbs. Fat from your meals is used for fuel instead of being immediately stored away in fat cells. You can feel free to eat high-fat (even saturated fat) foods! It’s a perfectly healthy choice, as long as you don’t eat them together with refined carbs.

Insulin, as you’ll recall, suppresses the action of the enzyme LPL on muscle cells and prevents them from pulling in glucose from the bloodstream. Less insulin present in the bloodstream means less suppression of LPL on muscle cells. Without that suppression, the muscle cells are free to pull in fatty acids from the blood and burn them for fuel. The enzyme HSL is also free to do its job when insulin is not present: Stored triglycerides in your fat cells can be broken down into fatty acids and released for fuel. Just by reducing the amount of insulin in your blood, you're more likely to burn fat instead of storing it!

Other things are happening in your body as well. When your carb intake is limited over a prolonged period of time, your body starts using up all that stored glycogen. Your body uses the glycogen stores preferentially because glycogen is the storage form of glucose, and your system is accustomed to burning glucose for energy. Once glycogen is broken down into glucose, it can be used as fuel.

Those glycogen stores will eventually run out. If you don't replenish them (say by going on a carb bender), your body will have no choice but to switch over completely to an alternate fuel source—fat! It can do this because your insulin levels have gone down. Your fat is now highly accessible and can be used as your body's main source of fuel. If you stay the course and keep your carb levels low, your body will become a fat-burning factory!

Most of the cells and tissues in your body, excluding your brain, can use fatty acids for fuel. When you are consuming a high-carb diet, the brain uses glucose exclusively as its fuel source. When you are consuming a ketogenic or low-carb diet and not supplying your body with large amounts of glucose, your brain must use an alternate energy source: ketones.

When your body is burning mainly fat for fuel, your liver takes some of this fat and converts it into ketones for your brain to use as energy. When your brain is primarily using ketones as its fuel source, you are considered to be in a normal and natural state known as ketosis. Even when you're not following a low-carb diet, you enter ketosis every night during sleep, when you must live off the fat stored during the day. It has been found, in fact, that the brain runs more efficiently on ketones than it does on glucose. This makes sense from an evolutionary perspective. In the past, our hunter-gatherer ancestors would have spent most of their time in ketosis due to the relative absence of carbs in their diet. Far from being unhealthy, this is the way your body is meant to work!

Ketosis is often confused with ketoacidosis, a pathological metabolic state marked by extreme and uncontrolled ketosis. Ketoacidosis generally occurs in people with type 1 diabetes (and more rarely with type 2 diabetes) when the disease is poorly managed. People with type 1 diabetes can't produce insulin, and in the advanced stages of the disease, people with type 2 diabetes may lose this ability as well. Because there is no insulin in the bloodstream, glucose in the diet can't be taken up by cells to be used as fuel. Instead, the body begins using fat as fuel, which, as you now know, creates ketones. Because there is no insulin to interrupt this cycle, ketone production is uncontrolled and the buildup of ketones causes blood pH to drop drastically (that is, the blood becomes acidic). Ketone levels are 10-40 times higher in diabetic ketoacidosis compared to levels in a person on a low-carb diet. The symptoms of ketoacidosis range from nausea and stomach pain to coma and even death. The low levels of ketones found in people on low-carb diets are perfectly safe, completely normal, and produce no uncomfortable or dangerous symptoms.

Measuring Your Ketones

Ketone bodies are formed by ketogenesis when liver glycogen stores are gone. They are byproducts of fatty-acid breakdown in the liver. Ketone bodies flow from the liver to tissues outside of the liver. Your body produces three different types of ketones. Two out of the three ketone bodies are used as a source of energy in the heart and brain, while the third is a waste product excreted from the body in your urine. In the brain, ketones are a vital source of energy during fasting (for instance, when you are sleeping at night).

Acetoacetate

Acetoacetate can be used as an energy source by the brain when blood glucose is low.

D-3-Hydroxybutyrate

D-3-Hydroxybutyrate can be used as an energy source by the brain when blood glucose is low.

Acetone

Acetone will break down in 5 hours if it is not needed for energy and will be removed as waste. This "use it or lose it" factor contributes to much of the weight loss experienced in ketogenic diets.

If you’re interested in testing your ketone levels you can measure them with special urine-testing strips that can be found at most pharmacies. As an alternative, you can measure ketones using a blood-testing device that’s similar to the glucose meter used by people with diabetes. This device directly measures the amount of ketones you're producing for energy, but it is very expensive.

High-Carb Diet: Fat Is Stored

1. Foods that are high in refined carbohydrates cause your blood sugar to spike. Large amounts of insulin are then released to deal with the glucose.
2. Insulin tells your body to store fat, and at the same time traps the fat in your fat cells, preventing you from burning it as fuel.
3. The glucose provides only a short burst of energy. Your blood sugar rapidly drops due to the surge of insulin, and you feel hungry again. You crave more refined carbs, and the cycle begins again.

Ketogenic Diet: Fat Is Burned

1. Insulin is still released when you eat low-GL, fiber-rich carbohydrates, but it is released at a much slower and more controlled rate than when you eat meals high in refined carbs.
2. Lower levels of insulin mean your body is less likely to store fat. They also permit your body to release stored fat and use it for energy.
3. Your body burns fat for energy, so you lose weight.

By now, you should have a better idea of whether you're carbohydrate-sensitive. You’ve learned how insulin can work against you to pile on the pounds and why controlling insulin allows your body to burn up stored fat.