March - April 2007

The Latest Information Coming from the Friedman School of Nutrition Science and Policy at Tufts University

Study Examines Calorie Restriction and Glycemic Load

Boston — The first phase of a caloric restriction study in human subjects at the Jean Mayer US Department of Agriculture Human Nutrition Research Center on Aging ( USDA HNRCA) at Tufts University found evidence suggesting that calorie-restricted diets differing substantially in glycemic load can result in comparable long-term weight loss. The study, part of the multi-center Comprehensive Assessment of Long-term Effects of Restricting Intake of Energy (CALERIE) trial, funded by the National Institute on Aging, accounted for dietary factors that affect hunger and satiety, used laboratory techniques to measure adherence, and was the first of its kind to provide a complete set of meals and snacks to its participants. Recruitment is currently underway for participation in the second phase of the CALERIE study at Tufts, which will examine the relationship between calorie-restricted diets, aging, and age-related disease.

"Participants in our pilot study achieved and maintained comparable weight loss after one year, regardless of whether they were on a low-glycemic-load or a high-glycemic-load diet," says corresponding author Susan Roberts, PhD, director of the USDA HNRCA's Energy Metabolism Laboratory. "The goal was for both groups to restrict calories by 30 percent and, after one year, both groups had lost an average of 8 percent of their original body weight. We found that the two groups did not differ significantly in their average body fat loss, energy intake, metabolic rate, or reports of hunger and satiety."

The two study diets were carefully matched for factors known to influence food intake during weight-loss efforts, such as palatability, dietary variety, and fiber. "Because there was careful attention to factors that influence hunger and satiety, participants were generally satisfied on a calorie-restricted diet," says Roberts, who is also a professor at the Friedman School of Nutrition Science and Policy at Tufts.

Thirty-four overweight but otherwise healthy men and women were assigned randomly to a low-glycemic-load (LG) or high-glycemic-load (HG) diet. At six months, the LG group had lost an average of 10.4 percent body weight, while the HG group had lost an average of 9 percent body weight. By 12 months, participants in both the LG and HG groups had lost an average of 8 percent of their starting body weight.

"Unlike several other long-term studies, which have reported greater weight loss with LG diets at six months but no differences by 12 months, our data show no significant short-term or long-term differences," notes Sai Das, PhD, scientist at the USDA HNRCA and first author of the study. "However, we did detect a greater tendency for weight and body-fat regain among LG participants. This finding suggests that reduced calorie intake may be harder to sustain on LG diets over time."

The LG diet contained 40 percent carbohydrate, 30 percent fat, and 30 percent protein; while the HG diet contained 60 percent carbohydrate, 20 percent fat, and 20 percent protein. A food's glycemic load is a relative measure of how much carbohydrate is in the food and how quickly that food is converted in the body to blood sugar. Examples of foods provided as part of the LG diet include bean and barley stew, low-fat cottage cheese, and pumpernickel bread. The HG diet included foods like bagels, candied sweet potatoes and shepherd's pie with mashed potatoes.

Both diets were designed to restrict calories by 30 percent, relative to a person's baseline energy requirements, while providing the recommended amounts of vitamins, minerals, and essential fatty acids. All participants attended weekly behavioral support groups and met individually with a dietitian.

To measure objectively actual dietary intakes, the researchers used a laboratory technique involving doubly labeled water. They determined that both groups ate more calories than study foods provided; at six months the HG group averaged a 16 percent calorie-restricted diet and the LG group averaged a 17 percent calorie-restricted diet. Although participants did consume additional calories, the degree of non-adherence was not significantly different between the LG and HG groups when measured at various points throughout the study.

"An important difference between our study and other weight-loss trials is that we did not rely on self-reported intakes," says Das, who is also an assistant professor at the Friedman School. "Underreporting of caloric intake can vary between 5 and 50 percent. By providing the study food for the first six months, we did not have to worry as much about lifestyle factors like shopping and cooking habits interfering with dietary change."

Roberts previously conducted a pilot study showing that a diet's overall glycemic load may be an important determinant of weight loss for people with high levels of insulin secretion, such as people with diabetes. "We have observed that for some groups, glycemic load may impact weight loss. However, in terms of calorie-restricted diets, we see little difference among diets of varying glycemic load when we account for factors that affect dietary adherence."

This work was supported by a grant from the National Institute on Aging, part of the National Institutes of Health; the USDA; and the Boston Obesity Nutrition Research Center. For more information about ongoing recruitment for the second phase of the CALERIE study at Tufts, call (800) 738-7555, or visit http://hnrc.tufts.edu/1192109692477/HNRCA-Page-hnrca2w_1192109692483.html.

Das SK, Gilhooly CH, Golden JK, Pittas AG, Fuss PJ, Cheatham RA, Tyler S, Tsay M, McCrory MA, Lichtenstein AH, Dallal GE, Dutta C, Bhapkar MV, DeLany JP, Saltzman E, Roberts SB. American Journal of Clinical Nutrition; 2007 (April);85:1023-x. "Long-term effects of 2 energy-restricted diets differing in glycemic load on dietary adherence, body composition, and metabolism in CALERIE: a 1-y randomized controlled trial."

Study Finds Dietary Fat Interacts with Genes

Boston — Research published in the Journal of Molecular Medicine examines how calories from fat, carbohydrate, and protein might interact with genes to affect body mass index ( BMI), or body weight-for-height, and risk of obesity among adults in the Framingham Heart Study. Jose Ordovas, PhD, director of the Nutrition and Genomics Laboratory at the Jean Mayer US Department of Agriculture Human Nutrition Research Center on Aging ( USDA HNRCA ) at Tufts University, and colleagues analyzed several common gene variants known as single nucleotide polymorphisms (SNPs) of the apolipoprotein A5 gene (APOA5), which produces a protein (APOA5) involved in the metabolism of fats in the body. For 13 percent of people in the studywithaspecificSNP(-1131T>C), dietary fat intake was not significantly associated with BMI and risk of obesity.

We observed an interaction between APOA5 and dietary fat intake, but we did not see an interaction between APOA5 and carbohydrate or protein intake for any genetic variants of APOA5," says Ordovas, who is corresponding author of the study.

"For most people in this study, eating more fat was related to a higher BMI. However, for peoplewithaspecificSNP(-1131T>C), fat intake was not significantly related to BMI. This contradicts results for most of the study population, where high dietary fat intake was related to obesity," explains Ordovas, who is also a professor at the Friedman School of Nutrition Science and Policy at Tufts. "These results were true despite a person's age, sex, physical activity status, or the amount of total calories consumed."

Ordovas notes that a high fat intake may potentially have health ramifications other than increased weight. However, in terms of weight, "It seems there might be a lucky few—in this study, 13 percent—who can eat any combination of food and maintain a healthy BMI. Whether they eat cheesecake or four pieces of whole wheat bread will not make a difference in their body weight if the foods have the same amount of calories.

"We have all known people that do not watch what they eat, but usually don't see any effect on their weight," says Ordovas. "This is the first study that enables us to identify this segment of the population using information on this gene.

"This does not mean that it is impossible for peoplewiththespecificSNP(-1131T>C) to become obese," Ordovas continues. "While exact components of the diet may not be as critical to maintaining a healthy weight, excessive calories over time can still contribute to obesity. Also, since the specific SNP does not interact with carbohydrate or protein, and does not affect BMI when interacting with fat, it may be more problematic for people in this group to lose weight through dietary changes if they do, in fact, become obese. Our findings demonstrate that although genetics help to determine our risk of obesity, dietary and lifestyle habits are also important to consider."

Ordovas determined that the interactionbetweenthespecificSNP(-1131T7>C) and dietary fat was strongest for monounsaturated fatty acids (MUFAs), found in foods such as olive oil and canola oil. People with the specific SNP who consumed 11 percent or more of total calories as MUFAs had a lower likelihood of obesity. "Basically, it appeared that the interaction of the specific SNP with MUFAs was the reason that fat intake did not affect BMI for this group," says Ordovas. "This interaction between APOA5 and dietary MUFA intake may explain why the Mediterranean diet, which is rich in MUFAs, is not generally associated with an increase in body weight. However, more studies are needed to confirm this.

"At this point, everyone is encouraged to follow current guidelines that recommend a well-balanced, healthful diet in order to maintain a healthy BMI and to reduce risk of certain diseases. But we study nutrigenomics with the idea that we can pinpoint people who may be at higher risk for certain conditions like cardiovascular disease, allowing these individuals to proactively alter the way nutrition affects their genes," says Ordovas. "Once we are able to do this, we may develop several sets of guidelines for the public, based upon a person's genotype."

Ordovas concludes that, "The problems of obesity are complex and there is variability among people. This study contributes to our knowledge of how APOA5 works and adds to our understanding of genetics and dietary interventions."

In 2006, Ordovas received a USDA Secretary's Annual Honor Award for his significant contributions to the field of nutrigenomics. The award is the most prestigious given by the USDA. For more information on Ordovas' work at the USDA HNRCA, please see "Genes and Diet Linked to Risk Factors for Heart Disease" in the September/October 2006 issue of Friedman Nutrition Notes.

This work was supported by the National Heart, Lung, and Blood Institute of the National Institutes of Health; the USDA Agricultural Research Service; and by grants from the American Heart Association, the Ministerio de Educacion y Ciencia (Spain), and the Ministerio de Sanidad y Consumo (Spain).

Corella D, Lai C-Q, Demissie S, Cupples LA, Manning AK, Tucker KL, Ordovas JM. Journal of Molecular Medicine. 2007 (February);85(2):119-128. "APOA5 gene variation modulates the effects of dietary fat intake on body mass index and obesity risk in the Framingham Heart Study."

If you are a member of the media interested in learning more about these topics, or in speaking with a faculty member at the Friedman School of Nutrition Science and Policy at Tufts University, please contact Siobhan Gallagher at 617-636-6586.

The Gerald J. and Dorothy R. Friedman School of Nutrition Science and Policy at Tufts University is the only independent school of nutrition in the United States. The school's eight centers, which focus on questions relating to famine, hunger, poverty, and communications, are renowned for the application of scientific research to national and international policy. For two decades, the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University has studied the relationship between good nutrition and good health in aging populations. Tufts research scientists work with federal agencies to establish the USDA Dietary Guidelines, the Dietary Reference Intakes, and other significant public policies.