Economics, Health Care

Is a calorie a calorie?

First, a disclaimer: I’m not a physician, or medical authority of any kind. But, as a biology/environmental science guy who has battled with his weight all his life, I tend to keep track of this particular debate.

So I’ve been reading a new study on the maintenance of weight loss that was recently published in the Journal of the American Medical Association.

The study, “Effects of Dietary Composition on Energy Expenditure During Weight-Loss Maintenance,” by Cara Ebbeling et al., is being interpreted in a strange variety of ways on the internet.

CBS News says, “Low-glycemic diet may be best at keeping off pounds.”

USA Today says “low-carb diet burns the most calories in small study.”

In The Atlantic, nutritionist Marion Nestle opines that the diet studied by Ebelling and company might not work in the real world, and just repeats her regular advice to eat less food, and particularly, avoid sugar and starch. At least Nestle seems to have understood the study. Others, not so much.

So, as AEI’s resident science-guy, I thought I’d jot down my thoughts on the new study.

The question Team Ebbeling was looking at (in plain English) is, “after you’ve dieted off a bunch of pounds, will the nature of your subsequent eating pattern influence how much metabolic slowdown you’ll suffer?” They looked at people who took off 10-15% of their body weight on a controlled diet, and were then randomly assigned to three-types of calorie-controlled eating styles after the weight loss:

  • low-fat diet (60% of energy from carbohydrate, 20% from fat, 20% from protein);
  • low–glycemic index diet (40% from carbohydrate, 40% from fat, and 20% from protein); and
  • very low-carbohydrate diet (10% from carbohydrate, 60% from fat, and 30% from protein; low glycemic load).

The heroic dieters were kept on these diets for 4 weeks, and they were measured for two indicators of metabolic slow-down: resting energy expenditure, and total energy expenditure. (They were also measured for a bunch of other health indicators, such as cholesterol levels, inflammatory proteins and the like, but I’m not going to get into that, as the authors conclude that there were no clear patterns in that data.)

Here’s what Ebbeling and Co. found:

Compared with the pre–weight-loss baseline metabolic rate, the decrease in Resting Energy Expenditure was:

  • greatest with the low-fat diet: –205 Calories/day (range: –265 to –144);
  • intermediate with the low–glycemic index diet: –166 Calories/day (range: –227 to –106); and
  • least with the very low-carbohydrate diet: −138 Calories/day (range: –198 to –77).

The decrease in Total Energy Expenditure showed a similar pattern:

  • greatest with the low-fat diet: −423 Calories/day (range: –606 to –239);
  • intermediate with the low-glycemic index diet: −297 Calories/day (range:–479 to –115); and
  • least with the very low-carbohydrate diet:  −97 Calories/day (range:–281 to 86).

Interestingly, what’s not getting much coverage in the mainstream media is the effect on hunger, post weight-loss, of the new regimes:

Using a 10-cm visual analog scale, ratings of subjective hunger…obtained before breakfast did not differ significantly among the low-fat, low–glycemic index, and very low-carbohydrate diets.

As I read all this, it says that after you diet, you’re somewhat screwed, because your metabolism slows down, and you have to eat less food at the new weight than you could if you’d never put the pounds on and taken them off in the first place (I know this from experience!). But, the extent to which you’re screwed can be influenced by changing the composition of your subsequent way of eating.

If, after you lose weight, you follow the USDA approved low-fat diet, your metabolic rate will slow by over 400 Calories a day. In other words, if you calculate the number of calories that a “never-plumped-up” person can take in for your age, height, and weight, you’d have to eat 400 calories less per day than they could.

For me, that would equate to about 18% of what my “never gained/lost” doppelganger got to eat. In other words, once I’ve lost weight, I’m stuck eating a fifth less food than someone who is my same age, height, and weight, but who never put the surplus weight on and took it off  (which sucks, by the way).

On the other hand, if you go with a low-carb diet after you shed the pounds, your metabolic sluggishness is only 97 Calories a day. For me, that would only be a shortfall of 4% compared to my smug, “I never-got-fat nyah-nyah” comparison-guy. (That’s a deficit of one medium apple)

Again, I’m not a physician, but to me, the only fair reading of this study is, if you want to maintain weight loss after you’ve dieted, you’ll have an easier time of it on a very low-carb diet, you’ll have a moderately tough row to hoe on a low glycemic-index diet, and you’ll have a serious metabolic vig to pay if you listen to the USDA and Michelle Obama, and go with the low-fat diet they recommend.

I’ve never really believed the whole “a calorie is a calorie” thing simply because it defies normal biological and metabolic patterns. Individuals react wildly differently to the same dose of a medication, toxin, or recreational drug. Individuals have significantly different sensitivities to different hormones. A bee sting will bother Bob, but might kill Suzy. Why anyone would ever think that individuals wouldn’t vary based on whether they were metabolizing mostly fat, or mostly sugar, is the real mystery to me.

For my money, Gary Taubes is (by far) the best writer on the subject of diet.

Second disclaimer: I’ve lost about 40 pounds since January, following a low-carb, “paleo” diet).

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