June 1st, 2012
Reality Check: Stop Exercising and Eat Chocolate?
It’s been a terrific few days of medical news for lazy people and chocoholics.
First, a study in PLoS One provided ammunition to the exercise-averse crowd by claiming that exercise can actually be bad for some healthy people. As an added bonus, a story about the study was carried on the front page of the New York Times.
Less than a day later, in a moment that will be long treasured by chocoholics, a study in BMJ calculated that people with metabolic syndrome could reduce their risk for serious cardiovascular events like heart attacks and strokes by eating dark chocolate every day.
Let’s take a quick look at each study:
The exercise study used data from 1687 people who participated in one of six different exercise studies and found that a surprisingly large percentage of people had a significant adverse change in one of several important risk factors:
- Increase >24 pmol/L in fasting insulin: 8.3%
- Decrease <0.12 mmol/L in HDL cholesterol: 13.3%
- Increase >0.42 mmol/L in triglycerides: 10.3%
- Increase >10 mm Hg in systolic blood pressure: 12.2%
The researchers were unable to find any factors that helped predict which patients would have an adverse change. Approximately 7% of the people in the study had adverse changes in two or more risk factors. The researchers didn’t discuss whether the types of changes they observed might also have been found in people not in an exercise program.
The NIH’s Michael Lauer praised the study and told Times reporter Gina Kolata: “We do not know whether implementing exercise programs for unfit people assures better outcomes. That has not been established.”
Steve Nissen provided a sensible perspective on the study for MSNBC:
With any therapeutic intervention, there are always responders and non-responders. No intervention produces benefits in 100 percent of subjects. Biological systems are complex and many other factors can alter the response to any intervention.
Moving from the savory to the sweet course, the BMJ study reported that daily consumption of dark chocolate can prevent cardiovascular events in people with metabolic syndrome. Dark chocolate has been shown to lower blood pressure, and may have additional beneficial effects on lipids and other metabolic factors.
Australian researchers used a sophisticated mathematical model to estimate the effect of eating chocolate in people with metabolic syndrome who had a systolic blood pressure 121 mm Hg or higher and were not taking antihypertensive medication. They calculated that daily dark chocolate could prevent 8.5 CV events over 10 years in 1000 people with metabolic syndrome.
The researchers concluded that the findings of their study “suggest that the blood pressure lowering and lipid effects of plain dark chocolate could represent an effective and cost effective strategy for the prevention of cardiovascular disease in people with metabolic syndrome (and no diabetes).”
I’d like to call attention to one additional detail of the study. The authors note that they modeled a “best case scenario” that assumed 100% compliance. Normally I would be skeptical about this sort of assumption, but since we’re talking about chocolate I think we’re much more likely to see a problem of over-compliance rather than under-compliance. The authors acknowledge that their study did not include any of the other possible effects of dark chocolate, including its “additional caloric and glycemic load.” But in a study population of metabolic syndrome, and in a world in which obesity and diabetes are growing exponentially, this seems a strange omission.
It’s hard to imagine how these two studies might contribute to efforts to combat cardiovascular disease. Would anyone seriously suggest that exercise should not be recommended to the vast majority of people? Does anyone really believe that chocolate has an important role to play in curbing the impact of metabolic syndrome? These studies may provide a small addition to the academic literature on cardiovascular disease, but it’s difficult to see how they contribute to public health.
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