Views / Science Says

What's making us fat? Inside the sugar wars

Experts disagree on what's really driving the obesity epidemic.


What is making us fat? The reasons for the obesity epidemic are still a matter of debate, even among experts. It’s really hard to study the long-term effects of a given diet. Fat was once nutrition enemy number one, but now some critics are taking aim at sugar. Here are three different views.  

First, an important bit of context: What is insulin resistance?

You can think of the hormone insulin as a key that unlocks fat and muscle cells. Your body converts food into simple sugars. When you eat, your blood sugar spikes, and your pancreas releases insulin. Insulin brings your blood sugar down by encouraging muscle cells to absorb sugar and use it for energy, and fat cells to absorb sugar and store it as fat. If you have insulin resistance, you’ve built up a bit of a tolerance to insulin. You need to secrete more of it in order to have the same effect of your cells, making it harder to keep your blood sugar under control. Some experts, not all, believe insulin resistance is a major factor driving many chronic diseases, including obesity.

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A little bit of sugar is important. It makes food taste good. But there is no question, from dozens of studies in humans and animals, that sugar, and particularly fructose, causes insulin resistance.  When you develop insulin resistance, it can turn into a number of chronic conditions, including obesity and Type II diabetes. Too much fructose also causes high blood pressure and fatty liver disease. And the effects tend to be worse if you’re also eating a lot of fat and other carbohydrates. Fructose and sugar are a problem not just because of all the calories they contain. If you compare them to calories from, say, fat, the fructose calories are much more harmful. Bottom Line: Along with lack of exercise and overeating, sugar, and especially fructose, is one of the main reasons for our obesity epidemic. Adults should cap fructose intake at 50 g per day.

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For the past century or so, the worst we’ve said about sugar is that it’s empty calories. The idea was that you could exercise it away and balance it by eating less of other things. That is naïve. There’s a significant amount of evidence that sugar is a fundamental cause of the obesity and diabetes epidemics worldwide. Something in our diet and lifestyle is causing it, and sugar should be the prime suspect. We don’t say too much smoking causes lung cancer. We say smoking causes lung cancer. If I’m right, and I clearly think and hope I am, doctors are going to be telling you sugar is killing you, don’t eat it. Bottom line: Sugar kills; minimize your intake.

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Gary Taubes’s ideas are oversimplified. I’ve been doing research on obesity for a long time, so I’m very familiar with the arguments about sugar and insulin resistance. We develop insulin resistance as we gain more body fat. That is the body’s natural defence mechanism to stop you from gaining more fat. It’s one reason we tend to stay at a constant weight. But you usually won’t become insulin resistant to the point that insulin doesn’t work, unless you are prone to developing Type 2 diabetes. Bottom line: The amounts of carbs, fat, or other major nutrients in your diet don’t matter as much as excess calories do. That’s what causes weight gain.

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