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Science for Life: The Skinny on Fat
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 Okay, so this evening, we are going to talk about fat and its relationship to obesity and health. Simply put, obesity is just too much fat. In our bodies, we have billions and billions of cells, and some of those cells are specially designed to store fat. Those cells are called adipocytes or fat cells. They look like many other types of cells, except that they have a very large droplet of oily fat in the cytoplasm. Our fat tissue is full of these cells.
What is this fat or oil found in the fat cell? Most of it is a special kind called triglycerides. You might remember them from when your doctor measures your blood lipids. Triglycerides have a backbone chain of three carbons. Attached to this backbone are longer fatty acids called long-chain hydrocarbons. Gasoline is a different kind of long-chain hydrocarbon. And like gasoline, fats are a very efficient way to store energy.
Triglycerides are oily substances that require very little water for storage. A lot of energy can be stored in a small droplet. This is a very good thing: we use our fat tissue to store energy. We can sleep through the night without eating. When we run out of sugar supplies in our liver and muscles, we use fat. In prolonged fasts, fat is very important. Although fat storage is good, too much is not. Today, excess storage of energy as fat is fueling our epidemic of obesity.
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Why does this happen? It's complicated, and a lot of people are trying to figure it out. There are plenty of obese people who have few complications. However, we're learning that, if the fat cells are insufficient to store all that fat, and/or they have an inflammatory reaction to that fat, the fat can spill over into other tissues, such as liver or muscle, that might promote a diabetic state or heart dysfunction.
Diabetes in the U.S. basically mirrors body weight. More than 6% of Americans have adult-onset type II diabetes.
Diabetes is also a huge global problem, and the risk varies by country. For example, if you live in China, there's a predisposition, perhaps genetic or perhaps environmental, to developing diabetes. The current estimates are that 227 million people in the world will have adult diabetes by 2015.
Fatty liver disease is another serious consequence of excess fat. For the movie Super Size Me, Morgan Spurlock ate at McDonald's every day for a month. Basically, he doubled his caloric intake to 5000 calories and became essentially human foie gras. He got really sick, and the reason was he got a fatty liver. Fatty liver disease leads to inflammation, hepatitis, and eventually to cirrhosis.
Obesity can be understood as an energy balance problem. Normally, we take in about a million calories per year, and yet our weight remains stable. We have remarkable mechanisms in place to keep our body weight stable, and they control our food intake and how much we burn for heat or use for work.
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The Body Mass Index (BMI) can be used to determine the relative risk of heart attack associated with a person's weight status. Find your own BMI by locating your height and weight; the corresponding value in the bottom row indicates your BMI.
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How do we define too much fat? Skin calipers have been used for a long time. Catalogs and stores are full of machines that will measure fat. The National Institutes of Health advocate the simple use of a tape measure and something called body mass index (BMI). BMI is calculated by dividing your weight in kilograms by your height in meters squared.
The BMI charts will show if you are at an appropriate weight for your height or if you are overweight or obese. It is pretty good for populations, but it is not perfect. As a young man, Governor Schwarzenegger had a BMI of 33, but no one would have accused him of having excess body fat. But most of us don’t have that kind of problem.
In fact, in the United States in 2007, two out of three people are classified as overweight, and one in three is obese. Amazingly, this happened in only the last 17 years. Look at a movie from the 1930s or 1940s, and you might say, “Wow, those people look different.”
Even more sadly, it's not just adults who are getting fatter. Our children are getting fatter and at alarming rates. We indoctrinate them early into this culture. Watching computers and TV, rather than active play, is contributing to obesity. In some states, 15–16% of kids are obese. The excess weight portends a lifetime of obesity and its problems.
So what exactly is the problem? For perhaps the first time in human evolution, we have lots of energy stores. It's like having a big tank of gas. You can go a long distance on it and so forth. But the problem is that obesity brings with it a whole host of health problems, including high blood pressure, high cholesterol, type II adult diabetes, coronary heart disease, fatty liver disease, stroke, and gallbladder disease. Arthritis is made worse, and sleep problems and cancer are linked epidemiologically to obesity. Basically, if you're obese, you have a higher risk of dying prematurely. The one thing that prolongs life in mammalian species is caloric restriction and leanness.
Several of the health problems that I just mentioned are included in the metabolic syndrome. The metabolic syndrome includes abdominal obesity, a high plasma triglyceride level, a low HDL cholesterol, high blood pressure, or high fasting glucose. As defined by guidelines, if you have three of these, you have metabolic syndrome.
Nearly one out of three adults is estimated to have metabolic syndrome by this definition. If you are over 55, it's one out of two. If you have metabolic syndrome, you are at increased risk of heart disease and of developing full-blown type II diabetes, which dramatically increases your risk of heart disease. If you become overweight, your total risk of dying doubles.
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Normally these things are held in balance at a weight that is called a “set point.” To become fat, you have to have an imbalance. But once you are fat, you level off at that weight, and then you become back in balance. So obese people are not eating more chronically. They have reached a new set point, and the new set point is high. Unfortunately, when you get to that set point, it's very hard to “de-set” yourself.
What contributes to this food intake? We live in a society of caloric wealth right now, particularly in this country. We're surrounded by cheap calories of low nutrient value, such as high fructose corn syrup.
For example, let's imagine a McDonald's meal. A Big Mac is 560 calories. Let's add a large bag of French fries, not the Biggie fries, at 520 calories. A large Coke, not the Biggie Coke, is 310 calories. Apple pies are two for one, so we'll take two. This meal, which is not the super-size meal, is 1900 calories. All for six bucks.
As a frame of reference, the average adult needs about 1800 calories per day as a base, and more depending on how active you are. For most people, that's about 2000 to 2500 calories, and for me about 2800.
The 1900 calories from the McDonald's meal is more than my basal need just in one meal. That's pretty remarkable. So that only leaves me with 900 more calories for the rest of the day, and it's too easy to find those 900 calories and more.
Robert V. Farese, Jr., MD, is a senior investigator in the Gladstone Institute of Cardiovascular Disease.
· Dr. Bersot continues the conversation on the next page ·
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Science for Life lectures are delivered three times a year. To put your name on our mailing list for notice of upcoming events at Gladstone, please email us at sci4life@gladstone.ucsf.edu
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