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A number of research reports at the November annual meeting of the North American Association for the Study of Obesity (NAASO) in Las Vegas presented new information about the relationship between weight gain and the consumption of dietary fat, carbohydrates, and protein.
Results confirm the wisdom of consuming more fresh vegetables and fruits. It also turns out that a well-balanced diet full of these low-fat, water-rich foods is an effective approach to weight reduction.
Increased consumption of fat, not carbohydrates, is the key culprit in gaining weight, according to a study by WebMD Weight Loss Clinic. The year-long review analyzed the self-reported eating habits of 28,700 adults who visited the web site between March 2003 and April 2004. Using a 500-question survey, researchers evaluated daily caloric intake, broken down by the percentages that came from fat, carbohydrates, and protein, in addition to other dietary habits and lifestyle factors.
Subjects were divided into three groups determined by body mass index (BMI): healthy weight, overweight, and obese. Almost 84% of the women and 98.2% of the men were overweight or obese, based on a BMI of 25 kg/m2 or greater.
The results showed that higher intake of fat in both men and women, including total fat consumption and percentage of daily caloric intake, was associated with an increased BMI, while the amount of carbohydrates consumed did not correlate to increased BMI. The connection between fat consumption and being overweight was stronger in women than in men.
"Low- or no-carbohydrate diets can consequently become high in fat and lead to weight gain in the long term," says study co-author David Benchetrit, MD, product consultant to the WebMD Weight Loss Clinic and co-creator of LeDiet, on which the program is based.
The difference in daily caloric consumption between overweight and obese subjects was not significant, leading the researchers to conclude that even a slight increase in daily caloric intake can contribute to weight gain. The average caloric intake was 4% higher in overweight participants than in healthy-weight participants, and 12% higher in those who were obese.
CARBS VERSUS FATS
"There is no doubt with cutting back on carbs you can have more rapid weight loss, but when you look at people who keep weight off, they pick a low-fat diet," says American Obesity Association vice-president Judith S. Stern, ScD, RD, professor of nutrition and internal medicine at the University of California at Davis. "That doesn't mean you can't lose weight on the Atkins diet. The question is, can you keep it off? Because everybody loses weight, and they lose it again and again and again."
The WebMD study results indicate a need to continue talking to patients about the amount of fat they eat, the type of fat, and the fact that fat is more calorie dense, says Karmeen Kulkarni, MS, RD, BCADM, CDE of St. Mark's Hospital Diabetes Center in Salt Lake City.
"Paying attention to fat is still important, and encouraging our patients to watch fat intake and portions of fat is really important," says Kulkarni, president-elect of health care and education for the American Diabetes Association.
ENERGY DENSITY
A separate series of studies presented at the NAASO meeting also emphasized energy density and portion size. Barbara J. Rolls, PhD, chair of the nutrition department at Penn State's College of Health and Human Development, who directed the research, concludes that decreasing the energy density of one's diet by choosing more low-energy-dense, water-rich foods, such as fruits and vegetables, can be a sustainable weight-loss strategy without the need to count calories or fat grams.
After examining the diet patterns of 7,500 typical Americans and calculating their average daily energy density intake based on federal data from 1994 through 1996, Rolls and her team found that those who ate less-energy-dense food actually ate a greater volume of food (but drank less in beverages) and consumed fewer overall calories than those who ate more energy-dense food. The low-energy-density group weighed less, too.
Total energy consumed by subjects in the low-energy-density group was 1,850 calories, compared with 2,193 calories consumed by those in the high-energy-density group. Energy intake from food (1,544 vs. 1,799 calories) and from beverages (306 vs. 394 calories) was also less in the low-energy-density group.
When talking with patients, Rolls says she uses the term calorie density rather than energy density because some people presume with the word energy that higher is better. "With calories, it is clear that lower is better," she says.
WATER-RICH FOODS
A second study of 101 obese women, led by Rolls's colleague Julia Ello-Martin, a Penn State doctoral candidate in nutrition, showed that incorporating foods rich in water into a reduced-fat diet is more effective than just reducing fat.
Researchers randomized the women into two groups. The energy-density group received positive advice to increase water-rich foods and to choose reduced-fat foods. Recommended foods included fruits and vegetables, with an emphasis on non-starchy fruits (e.g., melons and berries) and vegetables (e.g., broccoli, tomatoes, and summer squash), legumes, whole grains, soups, and high-fiber and reduced-fat food (e.g., cheese made from 2% milk instead of whole milk). The advice also focused on modifying recipes to reduce fat (e.g., using applesauce in place of oil in baked goods) and using different cooking methods (e.g., grilling or broiling instead of frying). The reduced-fat group was counseled only with restrictive messages about limiting portions and eating less fat. Neither group was assigned limits on energy or fat intake, but both were instructed to eat freely based on the principles advised.
Both groups lost weight after the first 6 months of intervention, but subjects in the energy-density group lost an average of 21 pounds, compared with 15 pounds lost by the reduced-fat subjects.
Rolls says the results give new spin to the messages imparted for years by the health care community: Cut down on fat a bit; eat more fruits and vegetables.
"This basically gives people an excuse to eat healthy, to eat more fruits and veggies, even the much-maligned potato," she says. "The lower you go in fat, generally the bigger portion you get in terms of calories. If you eat a lot of fruits and vegetables, you can eat a fair amount of fat, because they counteract each other. You get a portion that's twice as big for [the] same number of calories."
It is a matter of changing to a common-sense eating routine, concurs Stern.
"It has to be part of your repertoire. For foods high in calories, just eat less of it," she says.
PROTEIN AND CARBS
For between-meal snacks, high protein staves off hunger and reduces food intake at the next meal by 5%, according to a small study of 23 female subjects conducted by Manny Noakes, PhD, and colleagues at Australia's Commonwealth Scientific and Industrial Research Organization.
The study also found that over the course of a day, women who ate a snack bar high in fat and refined carbohydrates had blood glucose levels 14% higher and insulin levels 12% higher than those who ate a high-protein snack bar. The authors conclude this was a result of the lower postprandial response and lower food intake at the meal following the snack for the high-protein group. Both snack bars had the same amount of calories.
Stern says it is known that protein is involved in satiety, but that she would like to know what happens for the next 24 hours. Is appetite reduction just at the next meal or is it long-term?
"The whole idea is energy balance. We have to see what happens over
the day, at the meal after next," Stern says. 
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