In a large-scale study, scientists have shown that exercise and good diet affect mortality independently, showing that you need both to stay healthy .
Is vigorous exercise special?
Exercise is good for you, and so is a healthy diet. Moreover, those are probably the only currently available interventions with a proven effect on healthspan and mortality. Do you really need both, when some people suggest that you can “outrun the bad diet” ?
While a couple of recent studies have shown that vigorous exercise can offset at least some of the detrimental effects of overfeeding , these studies were small-scale and had short durations, thus ignoring the slowly accumulating effects of a bad diet. Still, vigorous exercise, which is defined as exceeding 6 metabolic equivalents of task (METs) and includes such types of physical activity as running, mountain biking, and very quick walking, has been shown to convey unique health benefits.
You can calculate your personal MET numbers with this simple formula if you know the MET value of an activity. On the other hand, if you know how many calories per hour you are actually burning, you can divide that by your weight in kilograms to get your activity’s MET value. Most calories-per-hour estimates available online are only estimates, particularly if they do not include body weight.
Large sample and robust design
In this new study, a group of scientists, using UK Biobank data from more than 300,000 Brits, attempted to settle the question of whether vigorous exercise can replace a healthy diet. The researchers analyzed self-reported exercise and eating patterns and controlled for an impressive array of possible confounding variables, including age, sex, smoking status, and type of job. The participants were divided into quartiles according to the overall amount of physical activity (0–210, 211–450, 451–920, 921–5040 min/week) and according to the amount of vigorous physical activity (VPA) (0-9, 10–74, 75–149 and 150+ min/week).
The researchers employed several more safeguards for robustness. For instance, they tried to minimize the risk of “reverse causation”, when a lifestyle change is caused by an already existing health condition. Hence, people with baseline diagnoses of cardiovascular disease (CVD), cancer, or degenerative neurological disorder, as well as people who had abnormally low BMIs or chronic pain, were excluded.
The participants were also assigned a diet quality score from 0 (the worst) to 3 (the best), although the researchers then bundled the data into tertiles and not quartiles: low diet quality, medium diet quality, and high diet quality. Unfortunately, this score was very basic, only accounting for meeting or missing the recommended daily consumption targets for three food categories: fruits and vegetables, fish, and red and processed meat.
The researchers looked at all-cause mortality, cardiovascular mortality, and mortality from a subset or cancers related to physical activity, diet, and adiposity, collectively known as PDAR cancers. This subset includes bladder, breast, colorectal, stomach, kidney, liver, endometrial, esophageal, and pancreatic cancers that collectively account for almost 60% of all cancer mortality.
The results showed that over the relatively long follow-up period (a median of 11.2 years), higher levels of overall exercise at baseline were significantly inversely associated with all three mortality outcomes. Interestingly, while for all-cause and cancer mortality, the highest exercise quartile emerged as a winner, for CVD mortality, it was the second quartile, corresponding to moderate physical activity. VPA levels were also inversely correlated with CVD mortality, but not with cancer mortality, and here too, the lowest risk was observed for the two middle quartiles.
The correlation of diet quality index with all-cause and CVD mortality was statistically insignificant, but the people with the highest diet quality had 14% less risk of dying from PDAR cancers. The researchers suggest that both the oversimplified index and their attempts to control for a large number of variables might have moderated the correlation, and that the real correlation between diet quality and mortality is probably stronger, which would be in line with abundant previous research .
Importantly, physical activity and diet emerged as independent factors. The researchers found no additive effect and concluded that “overall, there is no evidence for high levels of physical activity, measured as MVPA (medium and vigorous physical activity) or VPA, fully offsetting low diet quality in any of the analyses; neither was there evidence for a higher diet quality index fully offsetting a lack of physical activity.”
Like any population study, this one has its strengths and weaknesses. While the enormous sample size increases robustness, the simplistic diet score and a lack of longitudinal data (measurements were only taken at baseline) work in the opposite direction. However, the results align with our best knowledge about healthy diet and exercise – that is, you probably need both. Another interesting question arising from the results is whether, as a few additional studies seem to suggest, too much vigorous exercise can be detrimental .
 Ding, D., Van Buskirk, J., Nguyen, B., Stamatakis, E., Elbarbary, M., Veronese, N., Clare, P. J., Lee, I. M., Ekelund, U., & Fontana, L. (2022). Physical activity, diet quality and all-cause cardiovascular disease and cancer mortality: a prospective study of 346 627 UK Biobank participants. British journal of sports medicine, bjsports-2021-105195. Advance online publication.
 Phillips, S. M., & Joyner, M. J. (2019). Out-running ‘bad’diets: beyond weight loss there is clear evidence of the benefits of physical activity. British journal of sports medicine, 53(14), 854-855.
 Walhin, J. P., Richardson, J. D., Betts, J. A., & Thompson, D. (2013). Exercise counteracts the effects of short‐term overfeeding and reduced physical activity independent of energy imbalance in healthy young men. The Journal of physiology, 591(24), 6231-6243.
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