Is fat but fit just a catchy headline?
In May a new study that hit the headlines suggested that being fat but fit is just a myth. Fat but fit is referring to people who are classified as obese (BMI>30) but are metabolically healthy, therefore not suffering by any obesity associated condition like type 2 diabetes or heart disease.
What astonished me though about this story is that this study was not published at the time. It was presented to scientific conference but it has not yet been published in a scientific journal. This means that the study was still subject to criticism by other scientists who they may well ask for more tests or different tests that could alter the results presented at the conference. The whole point of having your research published is that it is going to be reviewed by other scientists who will approve it, disapprove it or make suggestions on it (most common).
What have the scientists presented?
The researchers from Birmingham University, analysed data of 3.5 million British patients from 1995 to 2015. The analysis has shown that despite being at the beginning of the study metabolically healthy, obese people were still at higher risk or developing heart disease, strokes and heart failure compared to people of normal weight. Since the study is so big the results would probably be highly significant. As the study though is not yet published it is hard to understand how the scientists have taken into consideration other risk factors like diet, genetics, socioeconomic status, alcohol consumption or smoking. Another potential bias is the weight bias and stigma from healthcare professional, which is also linked with poor health outcomes. There is, also, the argument that BMI is not the best tool since the question was whether working out can play a protective role towards the development of disease independently to obesity. It is true that BMI does not take into account the body fat percentage or how fat is distributed. Physical exercise can increase muscle mass that weighs more than fat mass while improving glucose metabolism and increasing basal metabolic rate. More importantly BMI does not take into account cardiorespiratory function, a main outcome of his study. However, even if BMI may not say the whole story about individuals it is a great public health tool and the most commonly used. There is not one study without flaws; the main problem here is, that the study is not yet published thus we cannot draw conclusions or criticize it.
What does previous evidence suggest?
Another large study (1) in 1.3 million Swedish men has shown that even though aerobic fitness in late adolescence decreases the risk of premature death, however, however if an individual becomes obese the positive effects of exercise are canceled. The researchers suggested “low BMI early in life is more important than physical activity”.
A recent review (2), though, supported the health benefits of exercising even if weight loss does not occur simultaneously. The review refers to number of studies in the ‘90s that have shown that obese individuals who have a good cardiorespiratory condition -fit have lower heart disease risk compared to unfit normal weight individuals. Another study (3) looking at the data of 43,000 Americans showed that overweight people who were physically active were at the same risk to develop heart disease or cancer as their healthy weight counterparts. Similarly, in children moderate to high levels of cardiorespiratory fitness may improve the damage extra body fat can cause (4,5). Another important outcome is that overweight or obese individuals who exercise have 50% less chance of developing depression (6).
Overall, all the studies to present are observational whilst randomized control studies are needed in order to clarify how physical activity improved the health outcome in obese individuals without altering the weight.
So what is the message?
Obesity is not a disease but it does increase your risk to develop other diseases greatly. Prevention is always preferable and this is why it is so important to invest in early nutrition. Changes, though, can happen and an obese person can improve his quality of life and reduce the risk of disease development. Physical activity cannot counteract the damaging effects caused by increased fat mass; it is not a panacea. Changes in diet as well are mandatory in order to be able to lose weight and improve health. The benefits, though, of exercise are more than just weight loss. Sometimes improved well-being and fitness precede changes in weight. If you started exercising and following a healthier dietary plan; do not get discouraged by the scales if they move too slow, embrace getting stronger, be patient and changes will come. You are not alone!
1. Hogstrom, G., A. Nordstrom, and P. Nordstrom, Aerobic fitness in late adolescence and the risk of early death: a prospective cohort study of 1.3 million Swedish men. Int J Epidemiol, 2016. 45(4): p. 1159-1168.
2. Ortega, F.B., et al., The Fat but Fit paradox: what we know and don't know about it. Br J Sports Med, 2017.
3. Ortega, F.B., et al., The intriguing metabolically healthy but obese phenotype: cardiovascular prognosis and role of fitness. Eur Heart J, 2013. 34(5): p. 389-97.
4. DuBose, K.D., J.C. Eisenmann, and J.E. Donnelly, Aerobic fitness attenuates the metabolic syndrome score in normal-weight, at-risk-for-overweight, and overweight children. Pediatrics, 2007. 120(5): p. e1262-8.
5. Mesa, J.L., et al., Aerobic physical fitness in relation to blood lipids and fasting glycaemia in adolescents: influence of weight status. Nutr Metab Cardiovasc Dis, 2006. 16(4): p. 285-93.
6. Becofsky, K.M., et al., A prospective study of fitness, fatness, and depressive symptoms. Am J Epidemiol, 2015. 181(5): p. 311-20.