Health for life

A study that appeared in the March 6 issue of JAMA shed a favorable light on a diet that is, relative to USDA recommendations, lower in carbohydrate and higher in protein and fat.

Researchers randomly assigned overweight premenopausal women to one of 4 diets representing a range of carbohydrate intake: Atkins (low-carb), Zone, LEARN (follows USDA Food Guide Pyramid), and Ornish (high-carb). The women received instruction on the diets and were followed for a year.

They concluded:

"Women assigned to follow the Atkins diet, which had the lowest carbohydrate intake, lost more weight and experienced more favorable overall metabolic effects at 12 months than women assigned to follow the Zone, Ornish, or LEARN diets."

However, overall weight loss was minimal:



There was no difference in fasting glucose or insulin among the 4 groups. Women following the Atkins diet did experience a small reduction in systolic blood pressure relative to the other diets.

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For the study (abstract):
Comparison of the Atkins, Zone, Ornish, and LEARN Diets for Change in Weight and Related Risk Factors Among Overweight Premenopausal Women

News summaries:
And the Winner Is ... Well, Nobody
Atkins Beats Other Diet Plans In Study

New research shows that a Mediterranean-style diet and diets low in available carbohydrates can offer protection against type 2 diabetes. The study is published in Diabetologia, the journal of the European Association for the Study of Diabetes (EASD), and is by Dr Carlo La Vecchia, Mario Negri Institute of Pharmacological Research, Milan, Italy, and colleagues.

The authors studied patients from Greece who are part of the ongoing European Prospective Investigation into Cancer and nutrition (EPIC), led by Dr. Antonia Trichopoulou, from the University of Athens. From a total of 22,295 participants, actively followed up for just over 11 years, 2,330 cases of type 2 diabetes were recorded. To assess dietary habits, all participants completed a questionnaire, and the researchers constructed a 10-point Mediterranean diet score (MDS) and a similar scale to measure the available carbohydrate (or glycaemic load [GL]) of the diet.

People with an MDS of over 6 were 12% less likely to develop diabetes than those with the lowest MDS of 3 or under. Patients with the highest available carbohydrate in their diet were 21% more likely to develop diabetes than those with the lowest. A high MDS combined with low available carbohydrate reduced the chances of developing diabetes by 20% as compared with a diet low in MDS and high in GL.

The authors say: "The role of the Mediterranean diet in weight control is still controversial, and in most studies from Mediterranean countries the adherence to the Mediterranean diet was unrelated to overweight. This suggests that the protection of the Mediterranean diet against diabetes is not through weight control, but through several dietary characteristics of the Mediterranean diet. However, this issue is difficult to address in cohort studies because of the lack of information on weight changes during follow-up that are rarely recorded."

They point out that a particular feature of the Mediterranean diet is the use of extra virgin olive oil which leads to a high ratio of monounsaturated to saturated fatty acids. But again research here has been conflicting. One review of dietary fat and diabetes suggests that replacing saturated and trans fats with unsaturated fats has beneficial effects on insulin sensitivity and is likely to reduce the risk of type 2 diabetes. However, in a randomised trial of high-cardiovascular-risk individuals who were assigned to the Mediterranean diet supplemented with either free extra virgin olive oil or nuts and were compared with individuals on a low-fat diet (comparison group), there was no difference in diabetes occurrence between the two variants of the Mediterranean diet when compared with the comparison group.

Regarding GL, the authors say: "High GL diet leads to rapid rises in blood glucose and insulin levels. The chronically increased insulin demand may eventually result in pancreatic β cell failure and, as a consequence, impaired glucose tolerance and increased insulin resistance, which is a predictor of diabetes. A high dietary GL has also been unfavourably related to glycaemic control in individuals with diabetes."

They conclude: "A low GL diet that also adequately adheres to the principles of the traditional Mediterranean diet may reduce the incidence of type 2 diabetes.

Researchers reporting in the July 17 issue of the New England Journal of Medicine published results of their two-year investigation into three popular diets: A low-carbohydrate diet (based on Atkins guidelines), a Mediterranean diet, and a low-fat diet (based on American Heart Association guidelines).

The full study can be found at:

Weight Loss with a Low-Carbohydrate, Mediterranean, or Low-Fat Diet

Weight Loss

For weight loss, the low-carbohydrate and Mediterranean diets performed best, and were just about tied at 2 years:

• Low-carbohydrate Diet: 4.7 kg (approximately 10 pounds)
  
• Mediterranean Diet: 4.4 kg (approximately 10 pounds)
  
• American Heart Association (AHA) Diet: 2.9 kg (approximately 6 pounds)

Women did better on the Mediterranean diet, while men did better on the low-carbohydrate diet.

Diabetes

There was an unexpected finding that applied specifically to participants with diabetes. Fasting blood glucose of people with diabetes who followed the Mediterranean dropped an average of 32.8 mg/dl; while the fasting glucose of diabetics in the other groups increased by 1.2 mg/dl in the low-carb group and 12.1 mg/dl in the AHA group.

People with diabetes who followed the Mediterranean diet also had the lowest fasting insulin and lowest insulin resistance (HOMA-IR).

Differences Between Diets

All participants reduced their intake from baseline and were eating about the same amount of calories, 1500/day for women and 1800/day for men, regardless of group assignment. Physical activity also increased from baseline but was not different between groups.

The low-fat AHA diet derived about 30% of its calories from fat and 50% from carbohydrate. "The participants were counseled to consume low-fat grains, vegetables, fruits, and legumes and to limit their consumption of additional fats, sweets, and high-fat snacks."

The Mediterranean diet derived about 33% of its calories from fat and 50% from carbohydrate. This group had the highest ratio of monounsaturated-to-saturated fat, probably owing to olive oil and nut consumption: "the main sources of added fat were 30 to 45 g of olive oil and a handful of nuts (five to seven nuts, <20 g) per day." It was a diet "rich in vegetables and low in red meat, with poultry and fish replacing beef and lamb." Members also consumed the greatest amount of dietary fiber.

The low-carbohydrate diet derived about 39% of its calories from fat and 40% from carbohydrate. Members consumed the least amount of carbohydrates (consuming about 120 g/day after the first 2 months and throughout) and the most amount of fat, protein, and cholesterol. It diverged from Atkins protocol by advising vegetarian sources of fat and protein. This was the only diet that was unrestricted in calories. However, participants averaged about the same amount of calories as the other groups. Notably, even though limits were not placed on how much members of this group could eat, the low-carb group had the highest drop-out rate.

Conclusion

"Mediterranean and low-carbohydrate diets may be effective alternatives to low-fat diets. The more favorable effects on lipids (with the low-carbohydrate diet) and on glycemic control (with the Mediterranean diet) suggest that personal perences and metabolic considerations might inform individualized tailoring of dietary interventions."

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