Are moderate-protein diets better than low-protein diets for people with metabolic syndrome?

Moderate carbohydrate, moderate protein weight loss diet reduces cardiovascular disease risk compared to high carbohydrate, low protein diet in obese adults: A randomized clinical trial

Original source: Nutrition & Metabolism 2008, 5:30
Authors: Denise A Walker Lasker (corresponding author), Ellen M Evans, and Donald K Layman
Publication date: 7 November 2008
DOI (digital document ID): 10.1186/1743-7075-5-30
Requires subscription? No
Publicly-available abstract: Yes

Synopsis:
This study compares the effectiveness of the standard USDA Food Pyramid diet with a higher-protein, lower-carbohydrate diet for weight loss in general, for fat loss in particular, and for lowering the blood-based indicators of cardiovascular risk and insulin resistance. A total of 50 people completed the testing, split between the two dietary approaches.

Both diets under test had the same amount of calories, with about 30% of total calories coming from fats. Carbohydrates supplied about 55% of the Food Pyramid diet group's caloric intake, and protein, the remaining 15%. The people assigned to this group were instructed to eat whole grains for their bread products. About 30% of the high-protein group's calories came from protein, with the remaining 40% coming from carbohydrates. (This is the same protein-carbohydrate-fat distribution advocated by the Zone Diet.) This group was instructed to eat primarily "high quality protein", including lean meats, dairy, and eggs. Both groups had similar amounts of fruits and vegetables in their daily diets. All subjects were instructed on portion sizes, dietary substitutions, how to weigh foods, and how to keep a food diary. There was no difference in exercise between the two groups.

Baseline measurements (weight, body fat percentage, cholesterol, and postprandial insulin) were taken at the start of the experiment. The subjects followed their assigned diet plans for four months, at which time the same measurements were repeated.

• The moderate-protein group lost about 5 pounds more per person than the USDA group, and more of their weight loss was from fatty tissues.
• Fasting glucose levels were unchanged, but fasting insulin levels decreased in the moderate protein group, while it increased in the USDA group. In addition, postprandial insulin levels dropped 85% for the protein group, but only 50% for the Food Pyramid group. (High plasma insulin levels are indicative of insulin resistance, which is often a predecessor to Type 2 diabetes.)
  
• There was a greater drop in total cholesterol in the USDA group than in the protein group. LDL ("bad") cholesterol dropped in the USDA group but rose in the protein group; on the other hand, HDL ("good") cholesterol dropped in the USDA group but rose in the protein group. The protein group also showed greater improvement in triglyceride levels than the USDA group. (High triglyceride levels are associated with increased risk of heart attack.)
  

Reliability:
The study was small scale, with only 50 people completing the four-month study. While the two groups of subjects were selected to be closely-matched, there is still opportunity for the results to be skewed. An initial run-in period put all subjects on as close to an even footing as possible before the trial started.
The authors are associated with an accredited university; the paper was published in a peer-reviewed journal.
Longer-term studies of larger groups may be needed to determine the long-term safety and effectiveness of high-protein diets.

The principal investigator (Denise A Walker Lasker) received funding from the National Cattleman’s Beef Association, The Beef Board and Kraft Foods. Both Beef associations have a vested interest in increasing protein consumption (in the form of beef).
The investigators have made no comparison between a higher-fat restricted-carbohydrate diet and a higher-protein restricted-carbohydrate diet.

Practical Applications:
The 30/40/30 protein/carb/fat (PCF) ratio is the basis of the Zone Diet. While this diet is higher in protein than traditionally advised for people with diabetes, recent publications suggest that this is not as high a risk as formerly perceived.

For further reading:
WebMD evaluates the Zone Diet
Wikipedia entry on the Zone Diet

This synopsis was based on the entire article.

A possible reason for increased risk of infection of obese people and those with Type 2 diabetes

Interleukin-18 resistance in patients with obesity and type 2 diabetes mellitus
Original source: International Journal of Obesity (2008) Vol. 32, pp. 1407–1414
Authors: G R C Zilverschoon, C J Tack, L A B Joosten, B J Kullberg, J W M van der Meer and M G Netea (corresponding author)
Publication date: published online 22 July 2008
DOI (digital document ID): doi:10.1038/ijo.2008.109
Requires subscription? Not for this article
Publicly-available abstract: Yes

Synopsis:
Interleukin-18 (IL-18) is a signalling chemical (similar to hormones) that has a strong effect on stimulating interferon (IFN) release. It is produced by a number of different white blood cells and central nervous system cells. Interferon is an important chemical in fighting infections.

Higher levels of IL-18 have been shown to decrease abnormally large appetite and to improve insulin sensitivity. Interestingly, several studies have shown high levels of IL-18 in obese people with insulin resistance, and a recent study has demonstrated that a common version of the genes producing IL-18 is associated with a higher body mass index (weight) in people with type 2 diabetes or coronary heart disease. In addition, weight loss after bariatric surgery (such as gastric bypass or lapband) results in lowered blood concentrations of IL-18.

The investigators suspect that the cells of obese people and those with insulin resistant diabetes may have high levels of IL-18 because they do not respond as well to IL-18 as those of people of normal weight and who are not diabetic. To test this theory, they tested white blood cells of obese and Type 2 diabetes patients and compared them to those of lean, non-diabetic people, and measured their IFN production in relation to their IL-18 levels. They found that in the obese and the diabetic subjects, these cells respond poorly to IL-18 and produce less interferon. They also show impaired release of IFN after exposure to disease-carrying bacteria and fungi.

They conclude that the reduced response to IL-18 may be responsible for the increased susceptibility to infection among those who are obese or who have Type 2 diabetes.

Reliability:
The study was conducted with a small number of subjects: seventeen control subjects, eleven obese non-diabetic subjects, and fourteen subjects with Type 2/insulin-resistant diabetes. (The possibility of LADA or other autoimmune diseases was ruled out at the start of the study.) The smaller the number of subjects, the greater the possibility for skewed or atypical results. The research was published in a peer-reviewed journal, and the investigators are all associated with the a University Medical Center in the Netherlands. Based on the small number of subjects, the results should be considered to point in the direction of larger studies to confirm the investigators' results, as well as further research into why these cells have an impaired reaction to IL-18.

Practical Applications:
A confirmed pathway and reason for increased risk of infection among obese people and people with Type 2 diabetes could lead to therapy to reduce that risk and to better fight those infections that do occur. If insulin resistance and excessive appetite are also directly related to impaired IL-18 response, then improving that response could conceivably result in weight loss and improved insulin sensitivity as well.


This synopsis was based on the entire article.