Evidence on obesity and HIV prevention

As reported by Sandy Szwarc, the indefatigable Katherine Flegal has produced a stunning rebuff to the excesses of the diet zealots who are spinning up an ‘obesity epidemic’ (abetted by the World Health Organization).

Flegal and her colleague Barry Graubard have examined data from the huge HANES III survey of the U.S. population (1988 – 1994) which included a bunch of anthropometric measurements of a large sample of the population, in addition to body-weight. They then examined death certificates from the U.S. death registry that linked to the HANES III survey participants through the year 2000 to see who died when, and of what.

What they found is summarized in the PubMed abstract

“For the level equivalent to BMI <18.5, estimates of excess deaths ranged from 0.3% for waist-hip ratio to 2.4% for percentage body fat. All except waist circumference, waist-hip ratio, and waist-stature ratio were significantly greater than zero (P < 0.05). For the level equivalent to BMI 25 to <30, the percentage of excess deaths was 0.1% for percentage body fat and negative for all other variables; estimates were significantly below zero only for circumferences and waist-stature ratio. For the level equivalent to BMI > or = 30, estimates ranged from -1.7% for waist circumference to 1.5% for percentage of fat; none were significantly different from zero. Estimates for all-cause mortality, obesity-related causes of death, and other causes of death showed no statistically significant or systematic differences between BMI and other variables.”

In other words, no matter how you measure body shape—by ‘BMI’, hip-to-waist, waist circumference etc—the risks fat people face of dying from any cause is no greater than the risk faced by people of ‘normal’ weight. Like previous results, this study shows that skinny people may even have a slight disadvantage.

Sandy Szwarc reports that the authors went on to examine

“[D]eaths from 21 different “obesity-related” diseases, including: cardiovascular disease, cancers (colon cancer, breast cancer, esophageal cancer, uterine cancer, ovarian cancer, kidney cancer, or pancreatic cancer) and diabetes or kidney disease. For the low risk level of measurements, the associations with deaths “were all quite small and close to zero,” they wrote. There were no statistical associations for the intermediate levels. Finally, “for the obese level, none of the 21 differences would have been significant even at a P value of 0.05,” they reported.”

The HIV study: Esther Duflo looks at the evidence from two studies of different approaches to HIV education in rural Kenya. The first looked at pregnancy rates among unmarried teenage girls as a proxy for unprotected sexual activity. It found that in schools where teachers were trained in the officially sanctioned ABCD curriculum (“Abstain, Be faithful, use a Condom… or you Die”), the rates of pregnancy were about the same as they were in schools where the teachers had not been trained to deliver this prevention message

Duflo compares this result with the report of a program to deliver young women a much simpler message on the distribution of AIDs in Kenya by gender and age. The data clearly show that having unprotected sex with older men (‘sugar-daddies’) would be dangerous because the prevalence of AIDs in this group is much higher than among young men of similar age to the girls. This risk-reduction strategy is more effective.

“Teenage girls who benefited from this program reported having sex less frequently with older men and more often with boys their own age (with whom they use condoms more easily). After a year, the pregnancy rates were 5.5% in schools that had not received the program and 3.7% in schools that had received it. This reduction is mainly due to a 67% reduction in pregnancies with an older partner.”

Duflo surmises that the sterner risk-prevention strategy which covers basic medical facts about AIDS, HIV transmission, prevention (excluding condoms), abstinence before marriage and care for people living with AIDS attempts to convey a lot of information without actually imparting any “practical wisdom”.

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