Is Atkins Really The Best?

I came across a study the other day showing that Atkins dieters lost more weight over a one-year span than people following other popular diets, including the Zone, Dean Ornish's diet, and the LEARN diet.

However, one big problem with the way the study was done means that there's only one reliable conclusion we can draw from it... and it's NOT that the Atkins Diet delivers a faster rate of fat loss than the other three diets.

Researchers from Stanford University Medical School assigned 311 overweight and obese women to follow one of four diets — Atkins (very low in carbohydrate), Zone (low in carbohydrate), Ornish (high in carbohydrate) and LEARN (low in fat, high in carbohydrate, based on national guidelines) — for one year [1].

The women attended one-hour classes by registered dieticians once a week for eight weeks, and were responsible for preparing and buying all their own meals.

The study shows that weight loss was highest in the women following the Atkins diet (4.7 kilograms, 10.4 pounds) compared to the Zone (1.6 kilograms, 3.5 pounds), LEARN (2.2 kilograms, 5.7 pounds), and Ornish (2.6 kilograms, 4.8 pounds).

However, a closer look at the results reveals that while the Atkins group did get better results, an extra 2 kilograms (4.4 pounds) over the course of a year is certainly nothing to get excited about.

After two months, the Atkins group had already lost around 4 kilograms (8.8 pounds) while the other groups had lost about 2.5 kilograms

Over the next 10 months, the Zone, LEARN and Ornish group didn't lose any more weight. In contrast, the Atkins group lost about 2 kilograms more after six months. By 12 months they had started to regain some of the lost weight.

All four groups reported eating roughly the same number of calories and maintaining that reduced calorie intake over the length of the study. Average calorie intake by group and time point is shown in the table below.

This brings us to the main problem with the study, that of self-reported food intake. In other words, this was not a study where the diet was tightly controlled by the researchers. Basically, the participants read a book and had a few sessions with a dietitian before being left to their own devices.

Self-reported food intake is a notoriously inaccurate way to measure calorie intake, and there is data to show that people can underestimate their calorie intake by up to 50%. In other words, someone who says they're eating 1500 calories per day may be eating anywhere up to 3000 calories.

Are we really to believe that subjects on the Zone, LEARN and Ornish diets managed to maintain a reduced calorie intake for eight months yet lost no additional weight?

Although your metabolic rate does decline after a period of low-calorie dieting, it's unlikely that this drop is going to be big enough to completely offset the calorie deficit caused by the diet.

Yes, your rate of weight loss is going to slow down. But you still have a calorie deficit and you'll continue losing weight, albeit at a reduced rate.

According to the self-reported food intakes, subjects on the Atkins Diet ate roughly the same number of calories as subjects on the other diets, yet they lost more weight.

Although some have claimed that these results support the idea of a so-called "metabolic advantage," the most likely explanation is that participants were simply not reporting their calorie intake accurately.

The faster rate of weight loss in the Atkins group over the first two months could easily be due to the loss of water, which tends to increase in the early stage of a ketogenic, low-carbohydrate diet. Plus, we know that protein has the effect of suppressing appetite, which is one reason why people on protein-rich diets typically eat less.

Rather than showing any major advantage to one type of diet, I think the only thing this study really tells us is that sticking to a diet for any length of time is extremely hard. Which most of us knew anyway.

About the Author

Christian Finn holds a master's degree in exercise science, is a certified personal trainer and has been featured on BBC TV and radio, as well as in Men's Health, Men's Fitness, Muscle & Fitness, Fit Pro, Zest and other popular fitness magazines.

If you want better, faster results from the time you spend in the gym, click here now for instant access to his step-by-step muscle-building and fat-burning workout routines.

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Reference
1. Gardner, C.D., Kiazand, A., Alhassan, S., Kim, S., Stafford, R.S., Balise, R.R., Kraemer, H.C., & King, A.C. (2006). Comparison of the Atkins, Zone, Ornish, and LEARN diets for change in weight and related risk factors among overweight premenopausal women: the A TO Z Weight Loss Study: a randomized trial. Journal of the American Medical Association, 297, 969-977