Radio Freethinker

Vancouver's Number 1 Skeptical Podcast and Radio Show

You can be Fat as long as you’re Fit

Posted by Jenna Capyk on December 13, 2011

It seems like there’s always a new study popping up in the news about diet, fitness, obesity, etc. Granted, these are very important topics for public education as the overall sedentary trend in our society is beginning to look rather alarming. I saw a commercial this morning claiming that today’s elementary school kids have a shorter life expectancy, on average, that their parents! So while I think that studies about general health are important, all too often these studies mean next to nothing because of small sample sizes, poorly controlled experiments, or inappropriate study groups. A study in this week’s edition of Circulation, however, caught my eye. It had a relatively large sample size and seemed to use more than the usual rigour in the data analysis phase.

The crux of the study is that BMI (or Body Mass Index, a measure of how over- or underweight a person may be) doesn’t have a significant effect on mortality from cardiovascular disease or any other cause. This is in contrast to cardiovascular fitness (measured by a treadmill test) which is highly correlated with mortality. Basically: you can be fat as long as you’re fit.

This study is based on data from 14 345 men. This number is smaller than the over 16 000 men originally subjected to the experiment, as those with conditions like cardiovascular syndromes, cancer, or other obvious death-causing diseases were excluded. Other study rejects included those who were underweight, had unexplained weight fluctuations, showed an unusually low heart rate under a stress test, and a constellation of other indicators of subclinical disorders. All of the study participants had at least two physical evaluations over 6 years, from which researchers were able to glean their baseline stats for body weight and fitness, as well as the change over the study period. This period was followed by eleven years of followup where researchers looked at the death rates of the men from any cause and from cardiovascular disease, specifically.

The bottom line from this study: fitness trumps BMI when it comes to avoiding death. Nine hundred fourteen deaths were recorded in the followup period, 300 of which were from cardiovascular disease. Men who increased in fitness were significantly less likely to die during the followup period than those who had stable fitness levels or those who decreased. In fact, for every unit increase in fitness level, men were 15% less likely to die, and 19% less likely to die of cardiovascular disease. The kicker? No such correlation was observed for BMI changes, after accounting for fitness changes. That is to say that even if BMI increased, if fitness also increased the risk of death was still lower. Perhaps even more surprising, a decrease in fitness correlated with higher mortality no matter what the BMI was doing.

While the big numbers and stringent statistical analysis in this study make the findings pretty convincing, there are a couple of important factors to consider. Firstly, all of the participants were of middle to high socioeconomic status and college grads. They were almost all white men. Furthermore, they were slightly overweight on average, and less than ten percent were obese. It’s important to keep these factors in mind as the results may only be applicable to people in this group. For example, it’s known that people of Indian decent exhibit fatty tissue with different characteristics than Caucasian people and this can impact their risk factors for obesity-related complications. You might also notice I keep saying men, this is because women were not included in the study. Other obesity-related complications might also make BMI a better risk indicator for obese people as these conditions are more serious in more obese people. BMI has also been a controversial method for assessing body fat content and obesity, although the authors did test this by measuring body fat percentage by other methods.

Regardless of specific limitations, the findings of this study carry some pretty interesting implications for a significant proportion of the North American population. Firstly, while BMI is popularly associated with health, this would suggest that for the average-ish case, body weight is more correlative than causative with respect to overall health, and that being overweight might be a symptom of inactvitiy and poor fitness than a cause of mortality. Again, these findings are likely not to extrapolate well to the morbidly obese. The authors are careful not to overreach their real findings, and only suggest that physical activity is likely to be the top factor influencing fitness change (the alternative I suppose being magically aquiring fitness-related powers through pure will-power). They also note that a previous twin study performed in Sweden backs up their results as this group found that weight loss from dieting was associated with increased mortality, while weight loss due to physical activity was not.

The bottom line seems to be right in line with the public health mandates seeming to constantly come down the tube: get active, stay active, live longer. While “extreme caloric restriction” has been hailed by many as the proverbial elixir of life when it comes to longevity, it seems to me that enjoying a cheeseburger, or a nice plate of pancakes, after a good bike ride might be the way to go if you’re talking quality of life. Maybe Hal Johnson and JoAnn McLeod had it right all those years: stay fit and have fun!


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