Q. But then why did this school of thought survive?
A. In part, because the research cost so much! If Congress tells NIH to spend X billion testing whether a fatty diet causes heart disease, you better find out that it does. Positive results are good for funding. Negative results are important in science, but in politics it's a different story. It's a fundamental problem in how we do public health science.
Q. So this unproven concept became "fact."
A. Once all the work was done, the money spent, the scientists needed to convince us they were right. Soon, the idea took on a life of its own. One report after another came out about how dietary fat is killing people. Big front-page headlines in all the big papers. After a while we believed it because it seemed crazy not to.
Q. If their theory was wrong, why do we get fat?
A. We get fat because we disregulate our fat tissue. Particular nutrients in our diet do this.
A. Yes, carbs are key. Once people believed fat causes heart disease, the thought was that instead of eating fat we should go high carb. So the base of the famous food pyramid is all carbs — pasta, bread, potatoes. Interestingly, until the 1960s, the conventional wisdom was that these foods make you fat. My mother believed that. A quote I love from a 1960s medical journal is "Every woman knows carbohydrates are fattening." The joke is they were right. Carbs are fattening.
And in the 1960s, just as we were learning why carbs were unhealthy, we threw out the paradigm and replaced it with the idea they are lean heart-healthy diet foods. No surprise that this corresponds with the beginning of an obesity epidemic.
Q. How do carbs work in the body?
A. It has to do with the hormone insulin. Insulin works to make you store calories as fat in fat tissue. Insulin, in concert with higher blood sugar, is what makes a fat cell fat. And the more refined, easier to digest, sweeter the food you take in, the higher the insulin goes.
Q. Why do we crave carbs?
A. This is partly speculative. When you eat carbs, your blood sugar goes up. Insulin gets secreted, and your body tells your cells to burn that blood sugar first, storing the fat for later. Now, as insulin comes down, you should release the fat you stored and burn it next. But if insulin stays elevated, which is what happens from eating a lot of these high-carb foods — maybe, sweet foods and drinks, in particular — your body continues to tell lean tissue to burn carbs even if you don't have them to burn. So you crave them. It's as though there's only one nutrient your body can use, or wants, to burn for fuel — carbohydrates.
Q. Why do I crave Coke and cookies more than potatoes?
A. Sugar is special. Sugar triggers the same circuits in the brain that addictive drugs trigger.
Q. Kids love carbs. Are we setting them up for obesity by letting them feed their cravings?
A. It scares me to see how carb-obsessed children are. In the book I talk about a vicious cycle: As women get heavier during pregnancy, if they're obese or diabetic to begin with, or develop what's called gestational diabetes, they give birth to children who are more likely to become obese or diabetic when they become adults. Generation after generation. Fatter and more diabetic means higher insulin levels. So bodies learn to perceive carbs instead of fat as the best nutrients to burn much of the day. Are we giving birth to children who, each generation, are more carb-needy, dooming them to problems down the line? It's possible.
Q. Do you restrict your own kids' intake?
A. I try to keep them off sugar without being a zealot and keep refined sugars and carbs and starches to minimum. But given a choice, that's what they want. I hate seeing overweight kids whose parents are forcing them to run or reduce the size of their meals. They can't run because they're storing energy as fat. They're hungry because they're eating the wrong foods. The effort to slim them down by starving them or making them exercise is misguided. The problem isn't that they are sedentary. That's a side effect of the disregulation of their fat.