Reminder: Dietary Fat Does Not = Obesity

March 23, 2010 in Medicine by RangelMD

Yea. Dietary fat does not automatically and directly get deposited in your pudgy and unsightly areas.Yes, the fat in your unsightly areas is basically the same substance that is in the delicious parts of the animal remains you just ate (or the dairy product or plant oil in your food) but fats are biochemically interchangeable with carbohydrates (various sugars) via several common intermediates. Essentially, fat and carbs are just different forms of the same thing: energy.

Much of our dietary fat is broken down in the liver into sugars to be used in the body for energy. When the total dietary caloric intake (from both carbs and fats) exceeds the metabolic energy demands of the body, the excess is converted by the liver into fat and stored in adipose tissue in places such as the abdominal wall, the thighs and buttocks, and the ankles when all the other spaces are filled up. The reason for this is biochemical. Fat can store more energy at lower weight than glucose.

When the metabolic demands of the body exceed the dietary supply of calories, such as during periods of starvation or extreme fasting in the weeks before your 20th high school reunion, the body reverses the above process and converts fat into glucose to be used as cellular fuel. Of course, the actual process is far more complicated. Production and breakdown of fat is a constant process, the balance of which depends on the overall state of metabolism and this is highly dependent on the person’s overall activity level and dietary intake.

With all of this biochemical interchangeability, it makes no sense to believe that your body fat levels are mainly dependent on how much dietary fat you eat. Neither does it make much sense to suggest that your cholesterol levels are directly dependent on how much cholesterol you eat since, like fats, cholesterol is also biochemically interchangeable with glucose.

What does determine your fat and cholesterol levels? Ah, this is where it is not longer complicated. These are determined by your diet and activity levels. This why you can become enormous and develop high cholesterol levels by avoiding eggs, red meat, fatty foods, and exercise and eating a ton of foods rich in carbohydrates (breads, cereals, rice, potatoes). This is why it is perfectly possible forĀ  a highly trained athlete have less than 1% body fat and very low cholesterol levels despite a diet high in meats, fats, and eggs.

Why then does your doctor and government dietary guidelines always talk about a “low fat diet”? There is some indirect truth in avoiding a fatty diet. Fat tastes so good because it is high in energy and so may more easily lead to excessive caloric intake. But the real reason is that this simplistic “eating fat makes you fat” mantra took hold decades ago before medical science had really figured out what was going on. By the time the scientists pieced it together, the fat myth had become a convenient part of our obesity denial culture. It’s easier to believe that we can avoid obesity and eat all the donuts and ice cream we want just so long as we avoid dietary fat*. It’s also easier for doctors who never bothered to pay attention in medical school biochemistry to keep this myth going than to take the time to re-educate their patients.

*The same fallacy of thought regarding diet and weight also applies to fast food.

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