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What We Know about Obesity

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THE WORLD HEALTH Organization defines obesity as a state of “abnormal or excessive fat accumulation.” Today, it is a worldwide epidemic affecting all ages, genders, and ethnicities, and it’s worsening with each successive generation. My 93-year-old grandmother never met an obese person until recently. She knew of no overweight kids in her school, family, or social circles. My 60-year-old mother had almost no overweight classmates. When I went to school, I had a few overweight classmates. They weren’t unusual, but they weren’t common either. My children, however, have many overweight and even obese little buddies.

Worldwide, obesity has nearly tripled since 1975. By absolute numbers, the United States is the most obese country in the world, followed closely by China and India. By proportion of population, 50.8 percent of the Cook Islands in Oceania is obese, followed by Qatar at 42.3 percent and the United States at 33.7 percent, according to a 2017 report of obesity rates by country.¹

Obesity is commonly classified by the Body Mass Index (BMI), which compares weight to height but ignores factors such as muscle mass, age, and fat distribution. This definition limits the BMI’s overall accuracy, but it is generally a simple and useful measure.

Figure 4.1. Body Mass Index²

Ironically, the overriding concern of the 1970s was global hunger and the difficulty of increasing food production to avoid mass worldwide starvation. Yet, today we live with a global obesity epidemic that kills more people than does starvation. This slow-motion surge toward rampant obesity was completely unforeseen and has shocked most public health authorities. The resulting health consequences are dire. Having a BMI in the obese or extremely obese range is a risk factor for many serious health ailments, including PCOS, as well as the following:

•Heart disease

•Stroke

•Lung disease

•Diabetes

•Cancer

•Non-alcoholic fatty liver disease

•Gall bladder disease

•Osteoarthritis

•Pancreatitis

So how did this happen?

THE LINK BETWEEN DIET AND OBESITY

IN 1977 A U.S. Senate committee published a new set of dietary guidelines for Americans. Today, the U.S. Department of Health and Human Services and the U.S. Department of Agriculture (USDA) update and publish a new set every five years. To battle heart disease, which was the primary health concern in the 1970s, the guidelines recommended significant cuts to people’s consumption of dietary fat. Even as people became obese, these same guidelines were trotted out to do battle with this new enemy. The original 1980 food pyramid from the USDA suggested that Americans eat 6 to 11 servings of refined grains, such as bread, cereal, rice, and pasta every single day. I’m not sure that I know anybody who considers eating 11 slices of white bread daily to be a slimming diet. Yet this was the very diet recommended by the government of the United States and followed by other countries around the world. Virtually every health professional, doctor, and dietician in the world was soon giving this advice.

In addition to low-fat diets, the other big trend of the 1970s was the increase in leisure-time exercise. Before then, the idea of exercising for health or fun was as foreign as rap music to disco fans. Originally this advice was given to improve heart health, leading to a boom in “cardio” exercises such as aerobics and running. This advice was soon co-opted for weight loss as well, despite the utter lack of evidence supporting the efficacy of these exercise programs for weight loss.

Figure 4.2. The U.S. Department of Agriculture’s 1992 food pyramid³

Today, there are more gyms per capita than ever before. Local marathons and 10K races attract tens of thousands of runners. For most of her life, my grandmother never saw a gym. While exercise certainly has many health benefits (improved muscle tone, improved flexibility, increased bone mass, etc.), weight loss is not one of them. Scientific studies repeatedly confirm the minimal weight-loss effect of exercise programs. Two main reasons explain why. First, doing more exercise generally leads to eating more food, which will negate much of the weight-loss effects. They don’t say that you are “working up an appetite” for no reason. Second, doing more exercise reduces a person’s overall activity at other times of the day. For example, if you work a physically demanding job like construction for eight hours every day, then it is unlikely you will get home and decide to go on a 10K run just for fun. If you have been sitting in front of a computer all day, then that 10K run may sound quite appealing, but increasing leisure time exercise does not change total daily activity.

From the 1970s on, we have continued to believe that a low-fat diet combined with exercise will reduce weight and that people who are obese are just lacking in willpower. What we now know is that while what we eat does affect our weight, dietary fat is not the culprit. To understand why, we need to look at what happens to food when it enters the body.

DIGESTION: HOW THE BODY BREAKS DOWN FOOD

ALL FOODS ARE a combination of three major components called macronutrients:

1.Proteins

2.Dietary fats

3.Carbohydrates

In turn, each macronutrient is composed of smaller units or building blocks.

Proteins are chains of building blocks called amino acids. In the human body there are at least 20 amino acids, which can be combined to form thousands of different proteins. Nine amino acids are considered essential because the human body cannot synthesize them, which means they must be obtained through diet. If you don’t eat enough of these proteins, you will become malnourished. Food sources of protein include meats, poultry, and seafood; dairy milk, cheese, and yogurt; eggs; beans and legumes.

Dietary fats are molecules called triglycerides, which are composed of a glycerol backbone and three fatty acids. Certain types of fat are also considered essential and must be obtained through diet. These include the omega-3 and omega-6 fatty acids. Food sources of fats include oily fish; dairy milk, cheese, and yogurt; eggs; nuts and seeds; coconuts; avocados.

Carbohydrates are chains of sugars such as glucose, fructose, or lactose. Table sugar, called sucrose, is composed of one molecule of glucose linked to one molecule of fructose. Starches, like flour, are composed of long chains of glucose in the form of amylopectin or amylose. There are no essential carbohydrates. Food sources of carbohydrates include grains; fruits and vegetables; beans and legumes; energy drinks and alcohol.

Food also contains microscopic amounts of vitamins (A, B, C, D, E, K, etc.) and minerals (iron, copper, selenium, etc.), which are known as micronutrients.

Digestion is the process of breaking down macronutrients—proteins, dietary fats, and carbohydrates—into their smaller components for absorption by the body. The amino acids and fatty acids that make up proteins and fats, respectively, can be either used as building blocks for cell components or burned for energy. The sugars that make up carbohydrates are burned for energy, but they are not used to build other cell parts.

The chemical reactions involved in creating this energy and building cell parts are collectively called metabolism. And each macronutrient is metabolized differently. Why is this important? Because these differences affect how energy is stored and used.

Protein metabolism

Protein, like lean meat, is broken down into its component amino acids during digestion and transported to the liver. Amino acids are mainly used to rebuild proteins in blood cells, bone, muscle, connective tissue, skin, etc. Think of this process as being similar to taking the letters from a Scrabble board and reshuffling them to create new words. We eat animal and plant proteins, break them into amino acids, and then recombine them to form our own proteins.

The primary function of ingested protein is to rebuild cell components, and burning it for energy is only a secondary function. If you eat more protein than is needed for rebuilding, there is no way to store these extra amino acids. Instead, the liver changes them into glucose by a process called gluconeogenesis, or “the formation of new glucose.” (This word is derived from “gluco” meaning “glucose,” “neo” meaning “new,” and “genesis” meaning “the formation of.”) For an average American adult, an estimated 50 to 70 percent of ingested protein is turned into glucose for energy.⁴ However, this percentage varies greatly depending upon your body weight and how much protein you are eating.

Dietary protein takes significant processing by gluconeogenesis before it is converted to glucose. By this time, the body has activated multiple hormonal systems to deal with the expected increase in glucose availability. Thus, blood glucose remains stable even if you eat lots of protein.

Insulin is released when eating protein, especially in patients with type 2 diabetes, and signals the cell to start synthesizing new proteins. Certain animal proteins, such as the whey in dairy, generate almost as much of an insulin response as carbohydrates.

Fat metabolism

Digestion of dietary fat requires bile to mix and emulsify it. Bile is secreted by the liver, stored in the gallbladder, and released by the small intestine. Once the fat is absorbed by the small intestine, it is in droplets known as chylomicrons that are absorbed into the lymphatic system, which empties directly into the bloodstream. These chylomicrons are carried to fat cells called adipocytes, where they deliver a form of fat called triglycerides that are taken up for storage.

Dietary fat is absorbed more or less directly into our stores of body fat. While it may appear that dietary fat is far more conducive to increasing overall body fat, we will see later that this is not the case.

Carbohydrate metabolism

The chains of glucose found in carbohydrates are digested or broken into smaller units of glucose for absorption by the body. The speed of digestion and absorption depends upon many factors. Refined carbohydrates, such as grains like rice that have been husked or polished, are absorbed almost instantly because processing removes most of the associated fiber, proteins, and fats that slow absorption. Unrefined carbohydrates, such as beans and legumes, are absorbed more slowly because none of the fiber or protein has been removed. Also, grinding grains like wheat into a very fine flour increases the speed of absorption.

The specific type of carbohydrate also makes a difference. Wheat contains mainly amylopectin A, which is quickly and easily absorbed by the body. In contrast, beans and legumes are high in amylopectin C, which resists digestion by the human body and is incompletely absorbed. The amylopectin C that remains in the intestines is eaten by the gut microbiome, which produces gas and is responsible for the flatulence associated with these pulses.

Blood glucose rises quickly when eating refined carbohydrates, stimulating secretion of the hormone insulin from the pancreas. The insulin sends a signal that moves glucose into cells to be burned for energy. With glucose stored in the body’s cells, blood glucose levels return to normal.

Figure 4.3. Carbohydrate metabolism

THE FED STATE: HOW THE BODY STORES FOOD ENERGY

THE BODY HAS two complementary methods of energy storage:

1.Glycogen (in the liver)

2.Body fat (in the fat cells)

When you eat more carbohydrates or proteins than your body needs, insulin rises. As we’ve seen, these macronutrients are converted into glucose and sent into the bloodstream, which causes your blood glucose levels to rise. This increase in blood glucose signals your pancreas to produce insulin, which indicates the availability of food and puts the body into the “fed” state. All the cells of the body (liver, kidney, brain, heart, muscles, etc.) can now help themselves to this all-you-can-eat glucose buffet.

If some glucose is left over, it must be stored away for future use. This is a relatively simple process, since the body just links all the glucose molecules into a long, branched chain called glycogen and stores it in the liver. Glycogen is made and stored directly in the liver. Our muscles also store their own supply of glycogen, but this source can only be used by the muscles. In other words, the glycogen within muscles cannot be used, for example, by the kidneys. In contrast, the glycogen in the liver can supply any organ by releasing glucose into the bloodstream.

In the fed state, insulin goes up, signaling the body to store excess food energy as glycogen. Liver-glycogen stores, if full, last approximately 24 hours. When the body’s glycogen stores are full, the body must use a second form of energy storage for unused glucose. The excess glucose from the liver is converted into triglycerides, or body fat, through a process called “de novo lipogenesis,” or creation of new fat. (The word “de novo” means “from new” and “lipogenesis” means “creation of new fat.”) Some of the glucose from which this body fat is created may have come from carbohydrates and some from dietary protein, which was changed from protein to glucose through gluconeogenesis.

Regardless of where the excess glucose comes from, the liver creates new fat (triglycerides) but cannot store it. Fat is designed to be stored in fat cells (adipocytes), not the liver. So the liver packages these triglycerides together with some transport proteins and exports them as very low-density lipoprotein (VLDL). In the bloodstream, insulin increases a hormone known as lipoprotein lipase (LPL), which helps the triglycerides move out of the VLDL particle and into the adipocyte. This effectively transforms excess glucose into triglycerides and moves them to the appropriate fat cells for long-term storage. If the rate of new fat creation from de novo lipogenesis exceeds the export capacity of the liver, these triglycerides back up in the liver and cause nonalcoholic fatty liver disease.

Remember, this process is not the same as ingesting dietary fat. The fat we eat is broken down into chylomicrons, absorbed by the small intestine, and sent directly into the adipocytes. There is no processing within the liver, no insulin signaling, and no possibility of using the glycogen storage system, which is exclusively for glucose.

This entire storage process for fat is much more laborious compared with the relatively simple glycogen storage. So why have the two different systems? The glycogen and body fat systems for storing food energy complement each other perfectly. Glycogen is easy to get to and convenient, but limited in storage space. Body fat is harder to get to and inconvenient, but unlimited in storage space.

Think of glycogen like a wallet. You can move your cash into and out of your wallet without much difficulty, but you would not hold six months’ worth of cash in your wallet. Think of body fat like your bank account. It is more difficult to move money back and forth: you have to go to a bank machine or teller, put money in, and perhaps buy investments. Getting your money out as cash is also not so simple, because you need to go back to the bank to withdraw it. But you can store your life’s savings in a bank account without worry. This balance between short-term and long-term storage in the body also applies when you want to use that stored energy, as we’ll see next.

Figure 4.4. How the body stores food energy (calories)

THE FASTED STATE: HOW THE BODY USES STORED FOOD ENERGY

THE WORD “FASTING” may sound scary, but it simply refers to any time you are not eating. When you sleep, for example, you are fasting. In the fasted state, your body reverses its process for storing food. When insulin falls, as with fasting, the body breaks glycogen back down into individual glucose molecules to supply energy to the whole body. This is why we don’t die in our sleep every single night. “Breakfast” is literally the meal that breaks our fast, so you can see that fasting is a part of everyday life.

Put another way, at any given time our bodies exist in only one of two states: the fed state or the fasted state. Our body is either storing food energy or using it up. High insulin is the body’s signal to store incoming food energy. Low insulin is the body’s signal to use the stored food energy because no food is coming in. In the fasted state, we must rely on our stores of food energy to survive.