The Atkins Diet: What's right and what's wrong?

The debate over the Atkins Diet flared up again in the summer of 2003, following the publication of several studies showing that it accelerates weight loss compared to its low-fat, high-carbohydrate counterparts.

For some nutrition experts, the Atkins Diet is the equivalent of "dancing with the dietary devil." They argue that it runs contrary to the advice of most major health organizations, which advocate a diet relatively low in saturated fat and high in complex carbohydrates.

Atkins Diet

The swing back to the Atkins Diet (which was first made popular in the 1970s) is a response to the fact that a low-fat diet hasn't worked for many people.

Unfortunately, the sudden death of Robert Atkins, the result of a fall outside his New York clinic, deprived the dieting world of one of its more influential and controversial players at a time when the Atkins Diet is stimulating fresh interest.

So, what did Dr Atkins say to cause all this controversy?

1. The massive rise in obesity is caused not because people eat too much fat, but because they eat too many carbohydrates.

2. The best way to lose weight is not to eat less fat. Rather, the solution is to eat less carbohydrate.

Though billed as a "diet revolution," the principles on which the Atkins Diet is based are not new. In his book, Eat Fat Get Thin, Barry Groves points out that an English undertaker called William Banting published a small booklet about low-carbohydrate eating back in 1863. While Dr Atkins did a fantastic job at popularizing the low-carbohydrate diet, it wasn't something he invented.

Low-carbohydrate diets

In fact, low-carbohydrate diets, which you'll also see called ketogenic (pronounced key-toe-jen-ik) diets, have been used for over 70 years to treat intractable seizures in children with epilepsy. Studies show that the number and severity of seizures may decrease for more than two-thirds of children treated with the diet.

However, it's not true to say that obesity has risen despite the fact we're eating less fat. In 1988, for every 100 calories in the average male diet, 37 of those calories came from fat. By 1995, this figure had dropped to 33 calories. The trend was similar for women, where the percentage of fat calories dropped by roughly the same amount [1].

While the percentage of fat in the diet has dropped, the absolute amount has gone up. Back in 1988, men were eating an average of 95 grams of fat each day. By 1995, this figure had risen to 101 grams. The average daily fat intake for women has also risen, from 63 grams in 1988 to 66 grams in 1995.

The reason for these apparently conflicting results is that most people are simply eating more food! When nutrition experts began urging us to eat less fat, many compensated by eating more carbohydrates. The problem is that many fat-free foods have just as many calories as the original high-fat versions.

Between 1988 and 1995, daily calorie intake for men rose from 2,272 to 2,667 calories. That's an increase of 395 calories - roughly the same number of calories you'll find in a Snickers® bar. Women are also eating more, with energy intake rising from 1,543 to 1,758 calories daily.

Portion size

In other words, obesity is on the rise simply because people are eating more and doing less. One reason is that portion sizes have ballooned. Gathering data from a variety of sources, researchers Lisa Young and Marion Nestle report that portion sizes began to grow in the 1970's, and rose sharply in the 1980's [3]. In fact, portion sizes have continued to grow in parallel with expanding waistlines.

Differences in portion sizes are one reason why some countries have lower rates of obesity. Some evidence for this comes from research carried in the journal Psychological Science [2].

Researchers compared the size of restaurant meals in France and the United States. They weighed portions served at 11 comparable outlets in Paris and Philadelphia, including fast food restaurants, pizzerias and ice cream parlors. Americans received substantially more on their plate.

While the average Parisian portion weighed 277 grams (9.8 ounces), the Philadelphia equivalent came in at 346 grams (12.2 ounces). That's a 25% increase.

The difference was even starker when the researchers compared a number of well-known international chains with restaurants in Paris and Philadelphia. Meals in the US were consistently much larger. In Chinese restaurants, Americans receive up to 72% more than they would have been given if they ordered the same thing in France.

The researchers also compared bars of chocolate, cans of soft drink and hot dogs on either side of the Atlantic. Again, American portions were considerably larger. A bar of chocolate in Philadelphia was 41% bigger than the same product in Paris. A soft drink was 50% bigger and a hot dog was 63% larger.

In short, when it comes to explaining why obesity has risen over the past few decades, total calorie intake is probably more important than any one nutrient.

Weight loss

That said, many critics of the Atkins Diet were forced to think again following the publication of several trials in 2003. The three studies, all of which lasted six months or longer, show greater weight loss following a low-carbohydrate rather than a low-fat diet. Cholesterol levels were not significantly affected by the diet.

Despite the questions raised by these findings, experts say they welcome these new results.

"This is good because it says that people can lose weight on the Atkins diet," says James Hill, Director of Clinical Nutrition at the University of Colorado and part of a team of scientists about to start a National Institutes of Health study of the Atkins diet.

"But we've seen this on almost any diet that has come along. You can go out and lose weight, but two to three years later, it has no effect. Atkins has been selling books for a bunch of years. I haven't seen much that says it has had a whole lot of impact on obesity."

It may be, says Hill, that some people do better with the Atkins approach and others lose more weight on a more traditional, low-fat diet. "We still know so little about weight loss," he said, "that I am willing to accept that we don't yet know the best way to help people succeed."

References
1. Kennedy, E.T., Bowman, S.A., & Powell, R. (1999). Dietary-fat intake in the US population. Journal of the American College of Nutrition, 18, 207-212
2. Rozin, P., Kabnick, K., Pete, E., Fischler, C., & Shields, C. (2003). The ecology of eating. Psychological Science, 14, 450-454
3. Young, L.R., & Nestle, M. (2002). The contribution of expanding portion sizes to the US obesity epidemic. American Journal of Public Health, 92, 246-249