The body mass index (BMI) of individuals who drink alcohol may be related to how much, and how often, they drink, according to a new study by researchers at the National Institutes of Health's National Institute on Alcohol Abuse and Alcoholism (NIAAA). In an analysis of data collected from more than 37,000 people who had never smoked, researchers found that BMI was associated with the number of drinks individuals consumed on the days they drank. Calculated as an individual's weight in kilograms divided by height in meters squared, BMI measures whether or not a person is at a healthy weight - low BMI values generally indicate leanness and higher BMI values indicate being overweight.
"In our study, men and women who drank the smallest quantity of alcohol - one drink per drinking day - with the greatest frequency - three to seven days per week - had the lowest BMI's," said first author Rosalind A. Breslow, Ph.D., "while those who infrequently consumed the greatest quantity had the highest BMIs." A report of the study by Dr. Breslow, an epidemiologist in NIAAA's Division of Epidemiology and Prevention Research and colleague Barbara A. Smothers, Ph.D., appears in the February 15, 2005, issue of the American Journal of Epidemiology.
"This is an important issue," said NIAAA Director Ting-Kai Li, M.D. "Obesity is prevalent in the United States and is a risk factor for numerous chronic illnesses and early death. Since alcohol use also is prevalent in this country, it is important to examine the relationship of quantity and frequency of consumption to body weight."
The researchers examined data collected from 1997 through 2001 in the National Health Interview Survey (NHIS), a nationally representative survey of the U.S. population conducted each year by the National Center for Health Statistics. Drs. Breslow and Smothers compared survey respondents' alcohol drinking patterns with their BMI scores. Since previous studies have shown that smoking and drinking interact to influence body weight, the current study looked only at current drinkers who had never smoked.
Results of previous examinations of the relationship between drinking alcohol and body weight have been inconsistent. The authors noted that one possible reason for this is that prior studies used a different way of assessing alcohol consumption than did the current study.
"Alcohol consumption consists of two components," explained Dr. Breslow, "the amount consumed on drinking days (quantity), and how often drinking days occur (frequency). Previous studies generally examined drinking based only on average volume consumed over time. However, average volume provides a limited description of alcohol consumption as it does not account for drinking patterns. For example, an average volume of 7 drinks per week could be achieved by consuming 1 drink each day or 7 drinks on a single day. Average volume may not fully explain important relations between quantity and frequency of drinking and health outcomes such as obesity."
The authors suggested several possible reasons for the observed associations of both quantity and frequency of alcohol use with BMI.
"Alcohol is a significant source of calories, and drinking may stimulate eating, particularly in social settings," said Dr. Breslow. "However, calories in liquids may fail to trigger the physiologic mechanism that produces the feeling of fullness. It is possible that, in the long-term, frequent drinkers may compensate for energy derived from alcohol by eating less, but even infrequent alcohol-related overeating could lead to weight gain over time."
Dr. Breslow cautioned against inferring cause-and-effect relationships regarding drinking frequency, quantity and body weight from this study. The study points to the need for prospectively designed studies to determine whether certain drinking patterns constitute risk factors for overweight and obesity.