September 13, 2011 (Lisbon, Portugal) — Results of a large population-based study show that high protein intake is associated with an increased incidence of type 2 diabetes. In presenting their results here at the European Association for the Study of Diabetes (EASD) 47th Annual Meeting, Swedish researchers suggested that replacing protein with carbohydrates, especially breads and cereals rich in fiber, might help prevent incident diabetes.
Diets low in carbohydrates but high in protein and fat have shown positive effects on weight reduction and glycemic control. Because studies have shown that high protein intake, especially animal protein such as processed meats, is associated with an increased risk for type 2 diabetes, the researchers thought it important to study the long-term risk for type 2 diabetes associated with the intake of various foods, food components, and nutrients.
Lead author Ulrika Ericson, MD, from the Department of Clinical Sciences at Lund University in Malmö, Sweden, told meeting delegates that the study consisted of 27,140 individuals (10,550 men) 45 to 73 years of age who participated in the Malmö Diet and Cancer study and who did not have diabetes at baseline. The researchers gathered information on weight, height, lifestyle, and socioeconomic factors. Dietary data were obtained from a 7-day registration of cooked meals, a detailed 168-item questionnaire covering other meals, and a 45-minute interview.
Between 1991 and 2006, 1709 incident cases of type 2 diabetes were identified. Using a Cox proportional hazards model, with adjustment for several potential confounders, the researchers calculated hazard ratios for diabetes incidence by quintiles of dietary intake, using the lowest quintile as the reference.
For both sexes, the groups "with the highest intake of protein were at increased risk" of developing diabetes in the future, Dr. Ericson told the audience. The researchers found a 37% increased risk for type 2 diabetes associated with the highest quintile of protein intake (hazard ratio [HR],1.37; 95% confidence interval, 1.17 to 1.61; P for trend < .001).
High intake of processed meat was also associated with an elevated risk for diabetes (P for trend = .01), as was intake of poultry and eggs. There was no association between diabetes risk and the intake of fish or red meat, but when all animal sources of dietary protein were considered together, an increased risk was seen. "This indicates that protein per se may be of importance," Dr. Ericson concluded.
"For carbohydrate intake, we did not find any overall association with type 2 diabetes," she said. "However, we found significant interaction with sex (P = .02). In men, high carbohydrate intake tended to be protective," reducing the risk for type 2 diabetes by about 23%. There was no significant effect of carbohydrate intake for women. Overall, fat intake was not associated with the risk for incident diabetes, but there was trend toward protection for women in the highest quintile of fat intake.
For both men and women, fiber intake was not associated with any change in risk (P for trend = .88), but the intake of fiber-rich breads and cereals showed a significant association with reduced risk for type 2 diabetes, with the highest quintile of intake having an HR of approximately 0.71 (P for trend = .002).
In summary, Dr. Ericson said a protective association exists with a high intake of fiber-rich breads and cereals. Although high protein intake has been shown to be effective for short-term weight loss and glycemic control, it is associated with an increased risk for type 2 diabetes. The results of this trial suggest caution when considering high-protein diets. However, she said, it is too early to make dietary recommendations on the basis of observed associations.
Session moderator Leszek Czupryniak, MD, PhD, from the Department of Diabetology and Internal Medicine at the Medical University of Lodz in Poland, told Medscape Medical News that a limitation of the study is its retrospective nature and its dependence on diary data derived from self-reports.
He said that high protein intake might facilitate type 2 diabetes and metabolic disturbances, mostly through the elevation of low-grade inflammation. However, such diets can facilitate weight loss, counterbalancing the increased risk. "But that needs a prospective study, not a retrospective analysis," Dr. Czupryniak advised.
Looking at the study as a whole, he said that eating a diet low in fat and high in plant fiber appears to be beneficial. "We're not sure about protein content of the diet; that probably depends on the condition of a subject" and on the person's genetics, which can affect response to a diet, Dr. Czupryniak said.
In the future, we will probably "need various diets for various genetic backgrounds, but we will have to be able to define it somehow," he observed.
The Swedish Research Council provided support for the study. Dr. Ericson and Dr. Czupryniak have disclosed no relevant financial relationships.
European Association for the Study of Diabetes (EASD) 47th Annual Meeting: Abstract 13. Presented September 13, 2011.
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