Eating whole grain foods is associated with a lower level of visceral adipose tissue (VAT), whereas consuming more refined grains is linked to a VAT increase, according to an article published online September 29 in the American Journal of Clinical Nutrition.

The findings are particularly important given that obesity rates are escalating. One third of Americans are currently obese and are therefore at higher risk for type 2 diabetes than others of normal weight.

“The economic burden associated with this epidemic is enormous, and estimated medical costs for an obese patient are 42% higher than for those who are normal weight,” write Nicola McKeown, PhD, from the Nutritional Epidemiology Program, Tufts University, Boston, Massachusetts, and colleagues.

Previous observational studies found a relationship between the consumption of 3 or more servings a day of whole grains — grains with intact ground, cracked, or flaked fruit — and decreased body mass index, abdominal fat, and tendency to gain weight.

In this subcutaneous adipose tissue (SAT)- and VAT-focused trial, known as the Framingham Study, 2834 subjects self-reported information about their food intake using a semiquantitative food-frequency questionnaire. Investigators measured the waists of the participants (49.4% of whom were women) ranging in age from 32 to 83 years. An 8-slice multidetecor computed tomography scanner was used to establish SAT and VAT volumes.

SAT, VAT Have Distinctive Associations With Whole and Refined Grains

The results showed that consumption of whole grain as well as refined grain foods were linked to both SAT and VAT volumes when these volumes were considered together. Otherwise, the only remaining associations were between whole grain and refined grain intake and VAT. That suggests that whole grain and refined grain foods each have different relationships associated with SAT and VAT.

Specific findings were as follows:

• A meaningful inverse association was found between the intake of whole grain foods and waist measurement (97.0 cm vs 93.7 cm in the lowest vs highest quintile category; P for trend < .001) after adjusting for age, sex, smoking status, total energy, and alcohol consumption.
• Only a marginally significant relationship with waist circumference was found regarding refined grain consumption (95.9 vs 97.3 cm; P for trend = .06).
• Whole grain consumption had an inverse association with SAT (2895 vs 2552 cm3 in the lowest compared with the highest quintile category; P for trend < .001) and VAT (1883 vs 1563 cm3; P for trend < .001).
• In multivariable models, refined grain intake demonstrated a positive relationship with SAT (2748 vs 2934 cm3; P for trend = .01) and VAT (1727 vs 1928 cm3; P for trend < .001).
• In joint evaluations, the SAT P value was attenuated (P = .28 for whole grains; P = .60 for refined grains), whereas VAT had a relationship with whole grains (P < .001) and refined grains (P < .001).

Interestingly, the investigators found that the value of whole grains appears to be undermined when refined grain foods still make up a large part of the diet.

“In conclusion, adults who consume ≥ 3 servings whole grains/d have significantly lower SAT and VAT compared with those who rarely consume whole-grain foods, but this beneficial association may be negated by higher refined-grain intake,” the authors write.

That suggested negation shows “there is no magic bullet here,” Connie Diekman, MEd, director of university nutrition at Washington University in St. Louis, Missouri, and immediate past president of the American Dietetic Association, told Medscape Medical News.

“The bottom line is how the whole diet comes together,” Diekman says. “It’s about keeping all grains to an appropriate calorie level — don’t all of a sudden add whole grains on top of what you’re already eating; make the shift from refined to whole grains.”

Pinpointing Causality Requires Further Study

The investigators stated several limitations to their research:

• Because all participants were white and older than 31 years, the results may not be representative of the larger population.
• Investigators could not rule out residual confounding with regard to lifestyle and dietary factors.
• Some food categories such as pasta and crackers were presumed to consist of refined grains, and consumption of whole grain varieties of these foods went unrecorded.
• The nature of the study did not allow researchers to determine causality between food intake and SAT/VAT volumes.

“Further research is required to elicit the potential mechanisms whereby whole- and refined-grain foods may influence body fat distribution,” the authors write. “There is a need for both prospective and dietary intervention studies before any firm conclusions can be drawn with regard to the influence of different types of grains and body fat depots.”

The US Department of Agriculture; the Framingham Heart Study of the National Heart, Lung, and Blood Institute of the National Institutes of Health; and the General Mills Bell Institute of Health and Nutrition, in Minneapolis, Minnesota, supported the study. The study authors have disclosed no relevant financial relationships. ConnieDiekman has performed consulting work for the Sara Lee Corporation.