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On Science: Eating your way to thin

This article first appeared in the St. Louis Beacon, April 22, 2009 - The Diet Wars are over. We live in a world where fat is common and thin is desired, a world where normal people, people like you and me, seek diets that will help us become less fat and more thin. But what diet should a well-meaning but only too human person pick?

Diet books are everywhere, suggesting very different ways for us to eat. Among the most highly touted are low carbohydrates diets like the Atkins Diet, the Zone diet and the South Beach Diet, low fat diets like the Ornish Diet and the National Heart Association Diet, restricted animal protein diets like the Mediterranean Diet and even fruit-intensive diets like the grapefruit diet.

At war with one another, every one of these diets claims to be superior to the others, to offer a simpler, easier and more effective way to lose weight. What is a reasonable person to do?

The Diet Wars really started in 1972, the year I graduated from college. I weighed 165 pounds then, rail thin for my height, and didn't give a thought to my weight. I certainly paid no attention to the new diet book published that year, THE ATKINS DIET REVOLUTION. Pushing a very low carbohydrate diet, the book became an immediate best seller. Much of this diet's success was due to word-of-mouth, as a lot of people who tried it lost weight.

Not me. Over the next 30 years I gained 30 pounds, and when I ran across the Atkins Diet a decade ago I tried it. As I explained in a column I wrote for the Beacon last spring, I lost 10 pounds very quickly - and then gained it all back.

It turns out it's hard to refrain from carbohydrates. At first lots of steak seems wonderful, but after a few months everything I was eating started to taste bland, and soon the smell of a peanut butter sandwich seemed like heaven. Eventually, defeated by my own appetites, I was back where I started, no thinner and a little more dejected, as if somehow the failure to loose weight was my fault.

My friends told me that I should try a diet that restrict carbohydrates less severely, like the Zone diet or the South Beach diet. I didn't, for reasons I explained in my Beacon column last year: All of these diets are based on bad science, making a claim that I knew as a biologist to be flat wrong. The claim? That it makes a difference WHAT you eat.

This couldn't be true, I reasoned. We gain weight when we consume more calories than we use, and store what's left as fat.

The chemical reactions involved in this conversion of excess calories to fat are all well known - I teach them to my biology students at Washington University and explain them in the textbooks I write. It's not rocket science: What matters is how many calories you consume, not whether you obtain them from carbohydrates, fat or grapefruit.

The two basic laws that no diet can successfully violate are:

  1. All calories are equal.
  2. (calories in) - (calories out) = fat

As Jennifer Levitz says pithily in the Wall Street Journal, "You aren't what you eat. You're how much."

A Matter of Quantity 

It's a little discouraging as a columnist to see how little impact you have when you publish an argument like this. People went right on buying the South Beach Diet. The Diet Wars continued unabated. The Internet is still alive with discussion of which diet is superior. My impact was limited, to say the least. But that doesn't mean I was wrong.

Now louder voices than mine have spoken. Two years ago The National Institutes of Health funded the largest-ever controlled study of weight loss methods, to address that one question: Are all calories equal?

The study assigned 811 overweight people in Boston and Baton Rouge, La., to one of four low-calorie diets. Each diet reduced calories about 750 calories a day from a person's normal diet, but the four diets involved different combinations of carbohydrates, fat and protein. All participants received counseling and were asked to exercise a fixed 90 minutes a week.

The results were published six weeks ago in the New England Journal of Medicine. Patients lost an average of 13 pounds after six months. After two years they had kept off all but 4 pounds, averaging a loss of 9 pounds and trimming two inches off their waists. Now get this. It didn't matter which group they were in. All four diets produced exactly the same results.

The take home lesson is thus a very simple one: To lose weight, exercise (increase "calories out") and count calories (reduce "calories in"). Count calories, not carbs.

What You Eat Matters

It does matter what you eat. There are a lot of "healthy heart" reasons to avoid excess fat in your diet, for example. We will all be healthier if we eat a more balanced diet. Being thin is not the same thing as being healthy.

But if thin is what you seek, there is wonderful news in this study: Many different diets will work for you. You can adopt one of the touted ones, or invent our own -- just don't eat so much. Counting calories is the road to a more slender you, but you can travel that road in whatever way you find easiest and most pleasurable.

Me, I still eat steak, but now there are a lot more salads in my life, now I enjoy meals more because I am hungrier - and I'm losing weight. Only 10 pounds so far, but this is a road I can travel.

George B. Johnson's "On Science" column looks at scientific issues and explains them in an accessible manner. 

Johnson, Ph.D., professor emeritus of Biology at Washington University, has taught biology and genetics to undergraduates for more than 30 years. Also professor of genetics at Washington University’s School of Medicine, Johnson is a student of population genetics and evolution, renowned for his pioneering studies of genetic variability. He has authored more than 50 scientific publications and seven texts.

As the founding director of The Living World, the education center at the St Louis Zoo, from 1987 to 1990, he was responsible for developing innovative high-tech exhibits and new educational programs.

Copyright George Johnson

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