A recent study conducted by U.S. and European researchers
have discovered that overweight and obese individuals were at no greater risk
for dying from heart disease and cancer compared to normal weight individuals,
as long as the overweight and obese individuals are metabolically fit. In the study researchers categorized obese
people that are metabolically fit if they were not insulin resistance, if they
did not have low levels of HDL (good cholesterol) and high triglycerides, and
did not have high blood pressure. The article then explains that almost half of
the obese participants qualified as metabolically fit. All individuals underwent blood tests,
physical exams, treadmill test, and completed questionnaires about their
lifestyle to determine cardiovascular fitness.
Overall, the results concluded that overweight yet metabolically fit
people were at a lower risk of early death from any cause than their thinner less
metabolically fit peers. Overall, I think
the study is very misleading. Since over 40,000 people enrolled in the study it is most likely that BMI was utilized to
determine at what weight individuals were considered overweight. As many know BMI does not take into account
muscle mass. It is possible that in the
study they recruited those who were considered overweight due to muscle mass,
but would actually have a low body fat percentage and a small hip-width
ratio. In order for people, fat or thin,
to be metabolically fit it is necessary to exercise and have a healthy
diet. Thin people are often considered
healthy; however even though they are at a healthy weight they can have high
cholesterol and diabetes due to poor diet and lack of exercise. This study would be more reliable if body
fat percentage or hip-width ratio were utilized to determine who belongs in the
overweight and obese categories. If
these tools were utilized I think those who were considered overweight and
obese yet metabolically fit based on BMI actually are not overweight. Many Americans,
thin or fat live a sedentary lifestyle and have a poor diet which makes them
metabolically unfit. Although the study
may suggest otherwise, being overweight, as in having high body fat, still is a
strong predictor of obesity related disease. Fitness is important for all people not only to maintain a healthy weight but to help your entire
body.
Interesting post on the use of BMI as an exposure measurement in epidemiological studies. I would agree with you in general that BMI can be a misleading surrogate measure of the more relevant measure of adiposity. Especially when trying to discern the obesity paradox! However, I think in the case of the studies cited in this Time article, with over 40,000 people enrolled, BMI as measured by self reported height and weight is of less concern as the sample size is large enough where the effect on the overall results by individuals who would be classified as overweight or obese due to muscle mass rather than adiposity is negligible.
ReplyDeleteAfter reading (briefly) two of the studies cited by the Time article, I would say my concern with the Time article is that first, their primary source on which they base their article off of has nothing to do with the obesity paradox and instead has to do with pregnancy outcomes in patients with heart disease, which makes me think they did not provide a correct link to their source. However, the more relevant point for me would not be the measure of BMI used in these studies, but would be the generalizability of these studies. Both studies cited by the Time article have cohorts that are not generalizable to the general population. The cohort of 40,000 pointed out at the beginning of the article were all part of a registry for people who had some coronary event, meaning these people are likely less healthy then the general population, and being metabolically active would be protective in such a case. In both articles, the study populations tend to be relatively older (60+), even though age was adjusted for, I think we'd both agree metabolism changes with age.
In conclusion, I think that BMI is a valid measure given the size of the study, both articles provide evidence of the obesity paradox on health, and lend interesting discussion topics on how BMI might be protective on various health outcomes in certain groups of people (with emphasis on certain groups of people).
Sources used for the times articles below: (Sorry, I was not able to post the actual PDFs for the articles)
http://eurheartj.oxfordjournals.org/content/early/2012/08/27/eurheartj.ehs217.full.pdf+html
http://jama.jamanetwork.com/article.aspx?articleid=209641
Jasmine,
ReplyDeleteYou have posted an interesting blog.
As Ryan pointed out, BMI is a surrogate measure for adiposity. A BMI defined as overweight (25-30) indicates, given a specific height, that an individual has excess body weight consisting of fat mass (FM) and lean mass (LM) factors, whereas obesity (30+) is simply suggestive of excess body weight that is FM. BMI as a measure of adiposity is limited because it does not explicate the distribution of adipose tissue. Please take a look at the following link (meta-analysis) for some more information regarding the validity (e.g. sensitivity and specificity) of BMI (Okorodudo, 2010). Succinctly, they concluded, “Commonly used BMI cutoff values to diagnose obesity have high specificity, but low sensitivity to identify adiposity, as they fail to identify half of the people with excess BF%.”
Hopefully in the future we will have easily available air displacement plethysmography (bod pods) to obtain absolute adipocyte volume. Nevertheless, this extraordinarily accurate measure is still limited because it doesn’t delineate between types of adipose tissues (e.g. VAT, SAT, IMLC content).
http://www.ncbi.nlm.nih.gov/pubmed/20125098
Sometimes I wonder if the people who review these articles say anything like, "Hmm, maybe BMI isn't the best way" or "That's weird, Americans and Europeans have a lot of variables in their culture to be included in the same study." You're totally right though, the study does seem misleading and an awful attempt to justify being overweight. Fitness is important for every bodily process, it should be a part of everyones routine. I wonder who funded this study as well, maybe by the candy industry or McDonalds?
ReplyDeleteI think it is important to note that the use of questionnaires pertaining to the lifestyle choices of the subjects participating in the study could lack in honest answers. Although, there were 40,000 subjects, and this high population could have helped normalize that factor. Also, I think it was crucial to have the blood and exercise tests performed. I feel like these examinations make the data more reliable than if only questionnaires were used.
ReplyDeleteOn another note, I would like to agree with Ashley in that the article seems like an "attempt to justify being overweight." I believe in my cardiology based physiology class, I learned that for larger bodies (those who weigh more), the heart is going to have to work harder to make sure the blood is distributed everywhere in the body that requires it. So even if overweight people have a healthier metabolism than some of those who weigh less, in the long run, I feel like they are going to have just as many- if not more- complications relating to heart disease: like high blood pressure for example.