Which Diet Works?
By MARK BITTMAN (New York Times June 26th 2012)
One of the challenges of arguing that hyperprocessed carbohydrates are largely responsible for the obesity pandemic (“epidemic” is no longer a strong enough word, say many experts) is the notion that “a calorie is a calorie.”
Accept that, and you buy into the contention that consuming 100 calories’ worth of sugar water (like Coke or Gatorade), white bread or French fries is the same as eating 100 calories of broccoli or beans. And Big Food — which has little interest in selling broccoli or beans — would have you believe that if you expend enough energy to work off those 100 calories, it simply doesn’t matter.
There’s an increasing body of evidence, however, that calories from highly processed carbohydrates like white flour (and of course sugar) provide calories that the body treats differently, spiking both blood sugar and insulin and causing us to retain fat instead of burning it off.
In other words, all calories are not alike.
You might need a little background here: To differentiate “bad” carbs from “good,” scientists use the term “glycemic index” (or “load”) to express the effect of the carbs on blood sugar. High glycemic diets cause problems by dramatically increasing blood sugar and insulin after meals; low glycemic diets don’t. Highly processed carbohydrates (even highly processed whole grains, like instant oatmeal and fluffy whole-grain breads) tend to make for higher glycemic diets; less processed grains, fruits, non-starchy vegetables, legumes and nuts — along with fat and protein — make for a lower glycemic diet.
A new study published Tuesday in the Journal of the American Medical Association adds powerfully to the notion that low glycemic diets are the way forward. (Or, actually, backward, since the low glycemic diet is largely traditional.) The work took place at the New Balance Foundation Obesity Prevention Center of Boston Children’s Hospital, and looked at people’s ability to maintain weight loss, which is far more difficult than losing weight. (Few people maintain even a small portion of their weight loss after dieting.) To do this, the researchers — led by the center’s associate director Cara Ebbeling and director David Ludwig — put three groups of people on diets to lose 10 to 15 percent of their body weight.
They then assigned each of the dieters, in random order, to follow four weeks each of three diets with the same number of calories. One was a standard low-fat diet: 60 percent carbohydrates — with an emphasis on fruits, vegetables and whole grains (but not unprocessed ones) — 20 percent from protein and 20 percent from fat. This is the low-fat diet that has been reigning “wisdom” for the last 30 years or more.
Another was an ultra-low-carb diet (for convenience, we’ll call this “Atkins”), of 10 percent of calories from carbs, 60 percent from fat and 30 percent from protein. And the third was a low glycemic diet, with 40 percent carbs — minimally processed grains, fruit, vegetables and legumes — 40 percent fat and 20 percent protein.
The results were impressive. Those on the “Atkins” diet burned 350 calories more per day — the equivalent of an hour of moderate exercise — than those on the standard low-fat diet. Those on the low-glycemic diet burned 150 calories more, roughly equivalent to an hour of light exercise.
Three conclusions you can draw on the face of this: One is that the kind of calories you eat does matter. Two, as Ludwig concludes, is that “the low-fat diet that has been the primary approach for more than a generation is actually the worst for most outcomes, with the worst effects on insulin resistance, triglycerides and HDL, or good cholesterol.” And three, we should all be eating an “Atkins” diet.
But not so fast; the “Atkins” diet also had marked problems. It raised levels of CRP (c-reactive protein), which is a measure of chronic inflammation, and cortisol, a hormone that mediates stress. “Both of these,” says Ludwig, “are tightly linked to long term-heart risk and mortality.”
His conclusion, then? “The ‘Atkins’ diet gives you the biggest metabolic benefit initially, but there are long-term downsides, and in practice, people have trouble sticking to low-carb diets. Over the long term, the low-glycemic diet appears to work the best, because you don’t have to eliminate an entire class of nutrients, which our research suggests is not only hard from a psychological perspective but may be wrong from a biological perspective.”
Almost every diet, from the radical no-carb-at-all notions to the tame (and sane) “Healthy Eating Plate” from Harvard, agrees on at least this notion: reduce, or even come close to eliminating, the amount of hyper-processed carbohydrates in your diet, because, quite simply, they’re bad for you. And if you look at statistics, at least a quarter of our calories come from added sugars (seven percent from beverages alone), white flour, white rice, white pasta … are you seeing a pattern here? (Oh, and white potatoes. And beer.)
So what’s Ludwig’s overall advice? “It’s time to reacquaint ourselves with minimally processed carbs. If you take three servings of refined carbohydrates and substitute one of fruit, one of beans and one of nuts, you could eliminate 50 percent of diet-related disease in the United States. These relatively modest changes can provide great benefit.”
The message is pretty simple: unprocessed foods give you a better chance of idealizing your weight — and your health. Because all calories are not created equal.