How much does weight loss independently affect health outcomes?
Fact or Fiction: Is obesity actually an epidemic? Part 4
In the last instalment of this series we saw that weight has an effect on quality and length of life at both the high and low ends of the BMI scale (1) (2).
Naturally this raises another question – if higher weight has negative health outcomes, does weight loss remedy them?
Does weight loss improve health?
It may surprise you to find out that out of the hundreds of weight loss studies that have been done, weight loss has NOT been shown consistently to prevent disease or improve quality of life in the long term. A systematic review of weight loss studies found that results of weight loss studies are mixed; some studies showed improvements with weight loss, others found no improvements, and still others found improvements with lifestyle changes in the absence of weight loss (2). Why such mixed results?
Long-term vs short-term weight loss
In the systematic review on weight loss, follow-up dates in studies ranged from 6 weeks to 5 years, with average studies being 2-4 years (2). It was noted that weight loss tends to have more benefit in the short term, with less long-term benefit to health (mainly because it can be difficult to maintain weight loss in the long term) (2).
A group out of the National Institutes for Health Researchers saw that weight loss was being recommended based on positive outcomes seen in short term trials and wanted to see if weight loss would have the same benefits in the long term (3).
This study gathered over 5000 participants in the US and randomized them to an intensive lifestyle intervention group (caloric restriction plus exercise) or control group (diabetes support and education).
Researchers found that in the short term the caloric restriction group experienced more improvements in diabetes measures, and greater improvements in cardiovascular risk factors. However, at the 9 year follow up, rate of cardiac events such as heart attacks or strokes was not significantly different between the two groups (3).
Why doesn’t weight loss have the expected long-term benefit?
Researchers have been asking this question for a long time, and have come to accept the “set-point” theory as an explanation. Weight is not a simple caloric intake vs expenditure equation – our bodies also physiologically adapt to “starvation states” (such as dieting). When your body is not getting enough calories to meet demands, it will slow down metabolism, decrease leptin (the “fullness” hormone), and become more efficient in exercise (4). This makes it difficult to keep weight off, or to continue to lose weight beyond a certain “set-point”.
So, if weight does have some modest effects on health, but weight loss doesn’t remedy them, what should we do instead? Tune in for the next post for some evidence-based health tips that aren’t focused on size or weight.
Sources:
Bhaskaran K, dos-Santos-Silva I, Leon DA, Douglas IJ, Smeeth L. Association of BMI with overall and cause-specific mortality: a population-based cohort study of 3·6 million adults in the UK. Lancet Diabetes Endocrinol. 2018 Dec;6(12):944–53.
Kolotkin RL, Andersen JR. A systematic review of reviews: exploring the relationship between obesity, weight loss and health-related quality of life: Quality of life systematic review of reviews. Clin Obes. 2017 Oct;7(5):273–89.
The Look AHEAD Research Group. Cardiovascular Effects of Intensive Lifestyle Intervention in Type 2 Diabetes. N Engl J Med. 2013 Jul 11;369(2):145–54.
Hall KD, Guo J. Obesity Energetics: Body Weight Regulation and the Effects of Diet Composition. Gastroenterology. 2017 May;152(7):1718-1727.e3.