Comparing 5 Diets on Long-Term Efficacy

Two recently published studies, taken together, would seem to provide, if not a crystal clear choice, at least a quite useful guide to choosing a weight loss plan. The first, a systematic review of the literature available on four popular diets, found little difference among them. Each was modestly effective in its own way. None in their modern forms were implicated in any significant cardiovascular or other health risk. The second study, a population-based cohort study looking at thousands of Nurses' Health Study participants, found that the Mediterranean diet is associated with a key indicator of healthy aging.

While this study did not address weight loss efficacy specifically, in terms of health and longevity, it appears the Mediterranean diet is an excellent choice. Given that weight regain over the long term was common among dieters choosing one of the four popular weight loss programs, the Mediterranean diet is most likely the best choice.

Popular Diets
The four diets in the review of 12 randomized, controlled studies—published online by the journal Circulation: Cardiovascular Quality and Outcomes—have endured long enough now to be elevated beyond “fad diet” status. Still, after a year, weight loss on the Atkins, South Beach and Zone diets failed to consistently outperform the control group. The fourth diet, Weight Watchers was the only one that did  better than the control group, but only modestly so: 7 to 13 lbs on Weight Watchers versus 2 to 12 lbs among controls.

Head to head, the Atkins and Zone diets performed similarly, but not very well, as noted above. And after two years, even the underwhelming but leading plan, Weight Watchers, could not escape backslide; some weight gain had occurred for both groups for whom data was available, Weight Watchers and Atkins. The review concludes: “Despite millions of dollars spent on popular commercial diets, data are conflicting and insufficient to identify one popular diet as being more beneficial than the others.” The second study comes to the rescue.

Mediterranean Diet
The “Mediterranean diet” refers to the region's tradition of consuming high proportions of fruits, nuts, vegetables, olive oil, unrefined grains and legumes; plus moderately high amounts of fish in proportion to meat and poultry. Saturated fat intake is proportionally much lower than that of monounsaturated fats. Consumption of dairy products is low. Rounding out the diet is a regular but moderate intake of alcohol (specifically wine with meals).

Many observational studies and intervention trials show a link between this diet and a reduction in overall mortality, reduced incidence of cardiovascular and other chronic disease, and an increased likelihood of healthy aging.

To better examine the last of these associations, researchers looked for the prevalence of DNA sequences called telomeres in people who do and do not adhere mainly to the Mediterranean diet.

Role of Telomeres
Telomeres inhabit the ends of chromosomes and help prevent the loss of DNA when a cell divides. Oxidative stress and inflammation accelerate the wearing down of telomeres' effectiveness to preserve the integrity of chromosomes. Telomere length is considered a biomarker of aging, with shorter telomeres associated with a decreased life expectancy and increased rates of chronic disease development. Telomere attrition appears to be modifiable, the researchers write, “as substantial variability exists in the rate of telomere shortening that is independent of chronological age.”

It's thought, then, that lifestyle choices like diet may well be a factor in determining telomere length. Since the Mediterranean diet is associated with antioxidant and anti-inflammatory effects, the study looked at whether adherence to this diet lengthened telomeres in people—in this case, U.S. women within the Nurses’ Health Study cohort.

Healthy Results
The study included 4,700 Nurses' Health Study participants who completed food-frequency questionnaires and who also had their telomere length measured. Women who adhered closely to a Mediterranean diet had longer telomeres after adjustment for characteristics likely to influence telomere length. These include age, BMI, smoking history and exercise frequency.

The authors calculated that the difference in telomere length among women who were more adherent to the Mediterranean diet could translate into an average gain of about 4.5 years of life. For promoting health and longevity, the Mediterranean diet is a winner. The researchers determined this extension in years as being roughly equivalent to the difference one would see with regular physical activity as opposed to only occasional activity. When combined with an active lifestyle, then, the longevity gains attainable with this diet could theoretically reach close to a whole decade of life. It is easy to see why these two choices would also almost certainly mean reaching a healthy weight and maintaining it in the long term, popular diets aside.

Circulation: Cardiovascular Quality and Outcomes, Nov. 11, 2014, http://circoutcomes.ahajournals.org/content/early/2014/11/11/CIRCOUTCOMES.

BMJ, 2014, 349: g6674, http://www.bmj.com/content/349/bmj.g6674

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