Size doesn’t matter. This is the conclusion of a newstudy exploring whether people with high body mass indexes (BMI) –those who are overweight or obese – are less likely to respondfavorably to HIV treatment. The data, published in the September issueof the Journal of Acquired Immune Deficiency Syndromes, refutesthe hypothesis that larger-than-average HIV-positive people may need tobe treated with higher doses of HIV medications to achieve durable viral load suppression and stable CD4 cell counts.

Studieshave demonstrated that BMI can influence the way drugs are metabolizedand distributed in the body. For example, a possible reason why womenmay be more likely to experience certain side effects – or have more severe side effect symptoms – isbecause their average body weights are lower than the average bodyweights of the males that make up the vast majority of dose-determiningclinical trials. In other words, some women may be taking higher dosesof a drug than they need, based on their lower body weight.

Onthe other end of the spectrum are people who are overweight or obese.The U.S. Centers for Disease Control’s HIV Outpatient Study (HOPS)conducted a study to evaluate whether overweight or obese HIV-positivepeople – who, like people of lower-than-average body weight may not be adequately represented in clinical trials – are more likely to experience treatment failure, due to the possibility of too little medication in their bodies.

Usingdata collected in HOPS, an ongoing cohort involving thousands ofHIV-positive people, Ellen Tedaldi, MD, and her colleagues analyzed theassociation of BMI with achieving an undetectable viral load andexperiencing a CD4 count increase of more than 100 cells after three tonine month of HIV treatment.

Among 711 patients includedin analysis, 43% had a BMI of more than 25, which is considered to beoverweight or obese.* Higher BMI was associated with being female,being black or Hispanic, being heterosexual, and using injection drugs.Although average pre-treatment viral loads were significantly lower inobese participants, overweight or obese BMI did not significantly alterthe likelihood of achieving an undetectable viral load and a CD4 cellcount increase of more than 100 cells compared with lower-weight studyparticipants.

In conclusion, Dr. Tedali’s groupindicated that a substantial proportion of the patients included in theHOPS analysis were overweight or obese. However, increased BMI was notassociated with decreased virologic or immunologic responses to HIVtreatment. This, they suggest, argues against the likelihood ofrequiring higher-dose treatment to manage HIV in larger-than-averagepatients.

Other studies, exploring the possibility ofusing lower-dose therapy in HIV-positive people with below-average bodyweights to potentially reduce the risk of side effects, have not yetbeen conducted.

* To calculate your BMI,first multiply your height in inches by your height in inches (e.g., 74” X74” = 5,476). Next divide that number into your body weight (e.g., 200/ 5476 = 0.0365). Finally multiple that number by 703 (0.0365 X 703 =25.66). This final number is your BMI. The National Heart, Lung, andBlood Institute has an automated calculator that can be used to calculate your BMI.

WhileBMI is considered to be a reliable indicator of total body fat, it doeshave some limits. It may overestimate body fat in people who havemuscular builds and may underestimate body fat in some people,including people with AIDS-related wasting, who have lost muscle mass.