Carbohydrates: The Cause of Overweight

Overweight is virtually always due to overeating carbohydrates.

There are three basic types of foods: carbohydrates, protein, and fat (plus vitamins and minerals, which don’t count when it comes to excess body fat). Examples of protein include beef, pork, poultry, fish, cheese, soy and eggs. Butter and cooking oil are examples of fat. Starchy and sweet foods are carbohydrates.

Examples of carbohydrates include:

•  Sweets
• Bread
• Pizza crust
• Cereal
• Fruit juice
• Sweetened soft drinks
• Buns
• Popcorn
• Crackers
• Potatoes
• Beans
• Corn
• Rice
• Chips

Everyone who is overweight is over-eating these types of foods. Everyone who breaks his diet does so with these types of foods. No one has an overweight problem due to overeating protein or fat. I will discuss why we have such strong cravings for carbohydrates in the next chapter. Right now, let’s discuss the biochemistry of how carbohydrates cause overweight.

Carbs Are Sugar

Carbohydrates are foods that are made of chains of sugar molecules. If the chain is short and composed of only a few (or just one) sugar molecules, they are called simple carbohydrates or sugars. If the chain is long and composed of many sugar molecules, they are called complex carbohydrates or starches. (In general, the shorter the chain of sugar molecules, the sweeter the taste.)

When we eat carbohydrates (whether sugars or starches) our saliva, stomach, and intestines break the sugar-chains apart into their individual sugar molecules. So, by the time a piece of bread (or popcorn, or pizza crust, or candy) reaches the end of our small intestine almost all that is left of it is simple sugar.

Once the carbohydrate is broken down into its sugar molecules, the sugar is next absorbed across the intestine and into the blood stream. When the sugar from the carbohydrates is absorbed into the blood stream it causes a rise in the blood sugar level. This begins a chain of events that can lead to problems.

Carbs Increase Insulin

As your blood sugar level increases shortly after you eat carbohydrates, your pancreas is stimulated to secrete the hormone insulin into your blood stream. Insulin causes blood sugar to go from the blood into your body’s cells (especially muscle and liver cells), and so the level of sugar in your blood stream goes back down. After your blood sugar level falls back to normal, the stimulus to the pancreas to secrete insulin also falls, and the secretion of insulin slows to a trickle. Here is a flow diagram of this process:

Carb intake → More blood sugar → More insulin → Less blood sugar → Less insulin

This system works well as long as we eat under about 150gm of carbohydrates per day (for reference, one tortilla has about 30gm carbohydrates). Problems begin when we eat more than 150gm of carbohydrates per day. Currently the average American eats 300gm to 500gm of carbohydrates per day—two or three times the healthy upper limit.

The more carbohydrates you eat, the more sugar you absorb into your blood stream. The more sugar you absorb into your blood stream, the more insulin is secreted by your pancreas (in order to pull all that sugar into muscle and liver cells). This high level of insulin begins to cause problems.

Too Much Insulin

If you eat 300gm to 500gm of carbohydrates per day, you absorb so much sugar into your blood stream that your insulin may have to stay at high levels all day in order to keep your blood sugar from being too high. Eventually, even first thing in the morning several hours after you’ve last eaten, your fasting insulin blood level will still be at a high level. In other words, at that point you’re keeping a high level of insulin 24 hours per day. This condition is called hyperinsulinemia.

For best overall health (according to researchers in longevity), our fasting insulin level should be below 10 IU/ml (one IU—International Unit—of insulin is 36 mcgm). Most laboratories consider “normal” fasting insulin levels to be anything below 20 IU/ml. However, it is common for Americans to have fasting insulin levels up to 110 IU/ml—more than 10 times the healthy upper limit. This is due to eating 300gm to 500gm of carbohydrates per day.

At high levels (the exact level depends on your genetics) insulin begins to cause several problems associated with being overweight. One problem is that the receptors for insulin on the cell membrane of muscle and liver cells become less responsive to insulin; this is called insulin resistance. These receptors are where insulin molecules actually attach to the cell to start the process of moving blood sugar into the cell.

Because of this reduced sensitivity to insulin, the receptors don’t efficiently move blood sugar into cells. As a result, your blood sugar remains higher longer because it isn’t being swept into muscle and liver cells as quickly as it should be.

This longer period of a high level of blood sugar stimulates the pancreas to secrete even more insulin. Then, this higher level of insulin eventually further reduces the sensitivity of insulin receptors, which again slows removal of sugar from the blood—which eventually increases insulin even more.

You can see that this is a vicious cycle: high carbohydrates → high blood sugars → high insulin → damage to insulin receptors → higher blood sugars → higher insulin → more damage to insulin receptors → even higher blood sugars → even higher insulin, and so on. This vicious cycle tends to get worse with age.

So, eventually, insulin secretion becomes a self-reinforcing process, leading to ever-higher insulin levels. This high level of insulin creates problems because insulin has other effects besides just moving sugar into muscle and liver cells. These other functions of insulin include

• Increasing fat storage and enlargement of fat cells
• Increasing the number of fat cells
• Increasing the blood level of “bad” cholesterol and triglycerides
• Increasing blood pressure

Let’s discuss each of these functions, and how they cause problems when insulin is too high.

High Insulin Causes Bigger Fat Cells

First of all, insulin stimulates fat in the blood stream to move into fat cells for storage. Insulin does this by activating an enzyme called lipoprotein lipase that lines the inside of blood vessels within fat tissue. When activated, lipoprotein lipase captures molecules of fat from the blood stream and transports the fat molecules out of the blood stream and into the adjacent fat cells for storage.

Even if we eat a low-fat diet, there is always plenty of fat in our blood stream; our liver makes fat and it keeps a normal level of fat in the blood. So, whenever lipoprotein lipase is activated by insulin it will find plenty of fat molecules to carry into fat cells for storage.

The more carbohydrates we eat, the more insulin we release into the blood stream, and so the more our lipoprotein lipase is activated to store fat in our fat cells. Our fat cells swell to accommodate more fat inflow. This is the first, and perhaps most powerful, way that excess carbohydrates leads to overweight.

High Insulin Causes More Fat Cells

Second, insulin stimulates the growth of new fat cells. Mixed in-between our mature fat cells we have very small cells called pre-adipocytes that don’t yet store fat, but that can become mature fat cells (adipocytes) that do store fat. One of the most powerful signals causing these pre-adipocytes to develop into mature fat cells is insulin. In fact, when scientists want to grow mature fat cells in a laboratory dish they stimulate pre-adipocytes with insulin.

So, the higher your level of insulin, the more of your pre-adipocytes will develop into mature fat cells. Each of these new mature fat cells then enlarges and stores more fat when high insulin activates lipoprotein lipase. This results in more overall body fat.

High Insulin Raises Bad Cholesterol

Third, insulin signals your liver to make more low-density (“bad”) cholesterol (VLDL and LDL cholesterol). This low-density cholesterol is responsible for the heart disease associated with being overweight. High insulin also lowers the “good” cholesterol (HDL) which protects against heart and blood vessel damage. The higher your HDL, the better. So, high insulin does double damage: raising bad cholesterol and lowering good cholesterol. Insulin also increases your triglyceride level, which is also bad for your heart.

High Insulin Causes High Blood Pressure

Finally, insulin stimulates the muscle cells in our arteries to thicken and to contract. This can cause high blood pressure. Insulin also causes us to retain water, which can further raise blood pressure.

This combination of problems—high insulin levels, high VLDL and LDL cholesterols, low HDL cholesterol, high blood pressure, and obesity—is called the Metabolic Syndrome. It is responsible for most of the more than 300,000 premature deaths annually in the US that are due to serious overweight. In fact, studies indicate that for every 30% increase in your average insulin level, there is a 70% increase in your risk of heart attack! A study of 7,000 men over a span of 15 years found that “the earliest marker of a higher risk of coronary heart disease mortality is an elevation of serum insulin level.”

For our discussion of overweight, the first two consequences of high insulin—storing more fat and making more fat cells—are the most problematic. Both lead to more total body fat.

Excess Carbs Turn to Fat

One more problem with eating excess carbs: blood sugar that we don’t burn for energy is converted by the liver into fat. This fat is then stored in our fat cells, leading to more weight. So, excess carbs promote body fat by both raising insulin thereby stimulating the fat-storage pump (lipoprotein lipase) and by providing more fat to be stored! It’s a double-whammy for weight gain.

The gist of what I have said so far in this chapter is this:

1. High levels of carbohydrates in the diet lead to excessive amounts of blood sugar
2. In response to excess blood sugar we secrete excess insulin
3. High levels of insulin damage the insulin receptors, which leads to even higher levels of insulin
4. High levels of insulin lead to the formation of more fat cells
5. High levels of insulin lead to more fat storage in each fat cell and an increase in total body fat
6. High levels of insulin lead to more VLDL and LDL (bad) cholesterols, less HDL (good) cholesterol, high triglycerides and higher blood pressure
7. Carbs not burned for energy are converted to fat for storage in fat cells

The process outlined above is a vicious cycle leading to steady weight gain as time goes by. Breaking this cycle is essential for permanently losing weight.

The “Food Pyramid” Mistake

The vicious cycle just described is why the “Food Pyramid” is so mistaken. The Food Pyramid encourages a high-carbohydrate diet. Most individuals who follow the Food Pyramid will eat 300gms to 500gms of carbohydrates per day—two to three times the healthy upper limit. The Food Pyramid was created from studies in the 1960s showing that a low-fat diet was healthier than a high-fat diet. Unfortunately, in those studies all the subjects—both the low-fat and the high-fat groups—were on high carb diets; the low-carb diet was not studied.

So, what the studies in the 1960s actually showed was that if you’re going to eat a high carb diet, then low fat is healthier than high fat. This is certainly true. What the studies couldn’t show was the benefits of a low-carb diet—because none of the subjects were on a low-carb diet.

Based on medical and governmental recommendations over the past 40 years, Americans have reduced the percent of fat in the average American diet by 30%. Over the same time, obesity has increased more than 50%. This is directly due to Americans eating more carbohydrates. Unwittingly, the US government has become a major carbohydrate “pusher” and a primary cause of overweight in the US.

Fortunately, the official position is slowly changing. The May 2002 issue of The Journal of the American Medical Association, a rather conservative medical publication, contained an article reviewing the evidence on low-carb (low glycemic index) diets. It concluded that there is good evidence of beneficial effects of low-carb diets on overweight, diabetes, and heart disease. The January 2003 issue of Scientific American had a 10-page article written by two Harvard professors recommending that the Food Pyramid be changed toward lower carb and higher protein and fat. Since 2000, several medical studies have compared the low-carb diet with low-fat diets, and the low-carb diet had better results in every case: better weight loss, less loss of muscle, and better blood chemistry values (including cholesterol values)—with none of the feared side effects.

Our High-Carb Culture

The American food culture has become based very heavily on carbohydrates. In fact, over 90% of the food offered in restaurants and grocery stores is starch or sugar. This is a significant increase since the 1960s.

Potatoes are part of nearly every meal. Bread is part of nearly every meal. Pasta is part of the diet nearly every day. Pizza is largely carbohydrate (the crust). Fast food burger restaurants push biggy fries and oversized hamburger buns. The most popular type of restaurant in the US is the Mexican restaurant, where 95% of what is served is almost pure starch, combined with fat.

The food advertising we’re exposed to on TV is virtually always for high-carb foods, from Eggos and Pop Tarts to pizza and candy bars. This advertising increases our carb-cravings and prompts us to eat carbs as soon as we can. TV cooking shows are largely about how to prepare irresistible carbohydrates.

A powerful part of our culture is the use of carbohydrates for socializing and recreation. A party without starches and sugars is no party at all, right? And eating starches and sugars has become the major form of daily entertainment for many Americans.

I often tell my patients that our current awareness of the carb health problem is at about the same level as our awareness of the tobacco health problem was in the early 1950s. At that time most American adults smoked, and we were just beginning to see the connection between smoking and lung diseases and various types of cancers. Over the next 50 years, our awareness of the dangers of tobacco increased dramatically, and we’ve seen a 180-degree change in the public’s attitude toward smoking. Nowadays, less than one in five Americans smoke.

I think that over the next 50 years we’ll develop the same awareness about the dangers of overeating carbs. We’ll see Americans strictly controlling their carb intake, and we’ll see the food industry changing to facilitate that. Eating lots of high-carb foods will be seen as an indication of having an addiction problem, a lot like the way cigarette smoking is viewed today.

Key Points

1. Overweight is virtually always due to overeating carbohydrates
2. All carbohydrates are digested into simple sugar
3. Carbohydrates cause a rise in blood insulin levels
4. Insulin activates lipoprotein lipase, which increases body fat storage
5. Insulin increases the number of mature fat cells—which then begin to store fat
6. High insulin damages insulin receptors, which leads to even higher insulin—the insulin resistance syndrome
7. High insulin raises the level of bad cholesterol and lowers good cholesterol, raises triglycerides and raises blood pressure
8. Excess carbs are converted by the liver to fat for storage
9. The food pyramid promotes a high carb diet, causing overweight
10. Our modern culture promotes eating excessive carbs every day; 90% of the food we are offered is carbohydrate

So far we’ve discussed how carbs lead to excess body fat. Now we need to discuss why we’re compelled to overeat carbs in the first place. The answer is that carbohydrates are not just a food. They have properties similar to addictive drugs. This leads us into the next chapter on “carb cravings.”