The Obesity Code: Unlocking the Secrets of Weight Loss (Why Intermittent Fasting Is the Key to Controlling Your Weight)

by Jason Fung

Insulin is a key regulator of energy metabolism, and it is one of the fundamental hormones that promote fat accumulation and storage.

At mealtimes, ingested carbohydrate leads to more glucose being available than needed. Insulin helps move this flood of glucose out of the bloodstream into storage for later use. We store this glucose by turning it into glycogen in the liver—a process called glycogenesis. (Genesis means “the creation of,” so this term means the creation of glycogen.) Glucose molecules are strung together in long chains to form glycogen. Insulin is the main stimulus of glycogenesis. We can convert glucose to glycogen and back again quite easily.

But the liver has only limited storage space for glycogen. Once full, excess carbohydrates will be turned into fat—a process called de novo lipogenesis. (De novo means “from new.” Lipogenesis means “making new fat.” De novo lipogenesis means “to make new fat.”) Several hours after a meal, blood sugars and insulin levels start to drop. Less glucose is available for use by the muscles, the brain and other organs. The liver starts to break down glycogen into glucose to release it into general circulation for energy—the glycogen-storage process in reverse. This happens most nights, assuming you don’t eat at night.

Glycogen is easily available, but in limited supply. During a short-term fast (“fast” meaning that you do not eat), your body has enough glycogen available to function. During a prolonged fast, your body can make new glucose from its fat stores—a process called gluconeogenesis (the “making of new sugar”). Fat is burned to r...

Insulin is a storage hormone. Ample intake of food leads to insulin release. Insulin then turns on storage of sugar and fat. When there is no intake of food, insulin levels ...

Glycogen is like your wallet. Money goes in and out constantly. The wallet is easily accessible, but can only hold a limited amount of money. Fat, however, is like the money in your bank account. It is harder to access that money, but there is an unlimited storage space for energy there in your account.

In other words, before you can even begin to burn fat, you start feeling hungry and anxious because your glycogen is becoming depleted. If you continually refill your glycogen stores, you never need to use your fat stores for energy.

OBESITY DEVELOPS WHEN the hypothalamus orders the body to increase fat mass to reach the desired body set weight. Available calories are diverted to increase fat, leaving the body short of energy (calories).

“We do not get fat because we overeat. We overeat because we get fat.” And why do we get fat? We get fat because our body set weight thermostat is set too high. Why? Because our insulin levels are too high.

Hormones are central to understanding obesity. Everything about human metabolism, including the body set weight, is hormonally regulated. A critical physiological variable such as body fatness is not left up to the vagaries of daily caloric intake and exercise. Instead, hormones precisely and tightly regulate body fat. We don’t consciously control our body weight any more than we control our heart rates, our basal metabolic rates, our body temperatures or our breathing. These are all automatically regulated, and so is our weight. Hormones tell us we are hungry (ghrelin). Hormones tell us we are full (peptide YY, cholecystokinin). Hormones increase energy expenditure (adrenalin). Hormones shut down energy expenditure (thyroid hormone).

Obesity is a hormonal dysregulation of fat accumulation. Calories are nothing more than the proximate cause of obesity. Obesity is...

Dr. Robert Lustig, a pediatric obesity specialist, believes that high insulin levels act as an inhibitor of leptin, the hormone that signals satiety. Leptin levels increase with body fat. This response acts on the hypothalamus in a negative feedback loop to decrease food intake and return the body to its ideal weight. However, because the brain becomes leptin resistant due to constant exposure, it does not reduce its signal to gain fat.30

In many ways, insulin and leptin are opposites. Insulin promotes fat storage. Leptin reduces fat storage.

With short-term physical stress, insulin and cortisol play opposite roles. Something quite different happens, though, when we’re under longterm psychological stress.

Under conditions of chronic stress, glucose levels remain high and there is no resolution to the stressor. Our blood glucose can remain elevated for months, triggering the release of insulin. Chronically elevated cortisol leads to increased insulin levels—as demonstrated by several studies.

Over time, insulin resistance (that is, impairment of the body’s ability to process insulin) also develops, mainly in the liver5 and skeletal muscle.

Stress contains neither calories nor carbohydrates, but can still lead to obesity. Long-term stress leads to long-term elevated cortisol levels, which leads to extra pounds. Reducing stress is difficult, but vitally important.

SLEEP DEPRIVATION IS a potent psychological stressor and thus stimulates cortisol. This, in turn, results in both high insulin levels and insulin resistance.

Sleep deprivation clearly will undermine weight loss efforts.

Perhaps eating refined carbohydrates leads to “food addictions.” Natural satiety signals are hormones that are extremely powerful deterrents to overeating.

Think about foods that people say they’re “addicted” to. Pasta, bread, cookies, chocolate, chips. Notice anything? All are highly refined carbohydrates. Does anybody ever say they are addicted to fish? Apples? Beef? Spinach? Not likely. Those are all delicious foods, but not addictive.

Consider some typical comfort foods. Macaroni and cheese. Pasta. Ice cream. Apple pie. Mashed potatoes. Pancakes. Notice anything? All are highly refined carbohydrates. There is evidence that these foods activate the reward systems in our brains, which gives us “comfort.” Refined carbohydrates are easy to become addicted to and overeat precisely because there are no natural satiety hormones for refined carbs. The reason, of course, is that refined carbohydrates are not natural foods but are instead highly processed. Their toxicity lies in that processing.

Dopamine hits.

When insulin (the key) no longer fits into the receptor (the lock), the cell is called insulin resistant. Because the fit is poor, the door does not open fully. As a result, less glucose enters. The cell senses that there is too little glucose inside. Instead, glucose is piling up outside the door. Starved for glucose, the cell demands more. To compensate, the body produces extra keys (insulin). The fit is still poor, but more doors are opened, allowing a normal amount of glucose to enter.

High levels alone do not lead to resistance. There are two requirements for resistance—high hormonal levels and constant stimulus.

In the case of insulin resistance, it comes down to both meal composition and meal timing—the two critical components of insulin resistance.

FUELING THE INCREASE in eating opportunities was the desire of big food companies to make more money.

So should we eat more fruits and vegetables? Yes, definitely. But only if they are replacing other unhealthier foods in your diet. Replace. Not add.16

Eat more carbohydrates. Eat more often. Eat breakfast. Eat more. Ironically, these dietary changes were prescribed to reduce heart disease, but instead, we’ve encouraged it since diabesity is one of the strongest risk factors for heart disease and stroke. We’ve been trying to put out a fire with gasoline.

Rewards reinforce behavior, and the behavior of eating is rewarded by the palatability—the deliciousness—of the food.

Food additives receive almost thirty times more in subsidies.

The government is subsidizing, with our own tax dollars, the very foods that are making us obese. Obesity is effectively the result of government policy.

almost every cell in the body can use glucose for energy, no cell has the ability to use fructose.

Once inside the body, only the liver can metabolize fructose. Where glucose can be dispersed throughout the body for use as energy, fructose is targeted like a guided missile to the liver.

The bottom line is that excess fructose is changed into fat in the liver. High levels of fructose will cause fatty liver. Fatty liver is absolutely crucial to the development of insulin resistance in the liver.

glucose is stored as glycogen in the liver, but the liver’s storage space for glycogen is limited. Once it’s full, excess glucose is stored as fat: that is, the liver begins manufacturing fat from glucose through de novo lipogenesis.

Sugars are not simply empty calories or refined carbohydrates. They are far more dangerous than that, as they stimulate both insulin and insulin resistance.

(80 percent).4 Agave’s low glycemic index was simply due to its high fructose content.

Despite having a minimal effect on blood sugars, both aspartame and stevia raised insulin levels higher even than table sugar.14

Therefore, after meals rich in fiber, blood glucose and insulin levels are slower to rise. In some studies, half the variance of the glucose response to starchy foods depended on their fiber content.5

short, fiber may decrease food intake, slow down food’s absorption in the stomach and small intestine, then help it exit quickly through the large intestines—all of which are potentially beneficial in treating obesity.

Short-term studies show that fiber increases satiety, reduces hunger and decreases caloric intake.

Soluble fiber reduces carbohydrate absorption, which in turn reduces blood glucose and insulin levels.

Removing protein and fat in the diet may lead to overconsumption. There are natural satiety hormones (peptide YY, cholecystokinin) that respond to protein and fat. Eating pure carbohydrate does not activate these systems and leads to overconsumption (the second-stomach phenomenon).

The processing and the addition of chemicals change the food into a form that our bodies have not evolved to handle. That is exactly why these foods are toxic.

Two teaspoons of vinegar taken with a high-carbohydrate meal lowers blood sugar and insulin by as much as 34 percent,

The cold storage may favor the development of resistant starch, and the vinegar adds to the benefits.

Blood glucose does not drive weight gain. But hormones—particularly insulin and cortisol—do.

Insulin causes obesity. The goal should therefore be to lower insulin levels—not glucose levels.

large observation studies do not link dairy to weight gain. If anything, dairy protects against weight gain, as

There are no intrinsically bad foods, only processed ones. The further you stray from real food, the more danger you are in.