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Will Exercise Make You Fat?



Dr. John Blundell

Dr. John Blundell

Yesterday, I had the pleasure of hosting John Blundell, at the Research in Progress seminar series at the Alberta Diabetes Institute.

Dr. Blundell is Professor of bio-psychology at the University of Leeds, UK, and is certainly one of the preeminent authorities on the bio-psychology of ingestive behaviour.

His presentation with the rather provocative title, “Will exercise make you fat?”, started with a broadside at the media, which lately has been quite active in promoting this notion.

However, as Blundell pointed out, this simplistic message is far from accurate in that the relationship between physical activity and its impact on ingestive behaviour and body weight is anything but straightforward.

For one, although short-term studies (days) do often show an increase in appetite, this is by no means regularly observed in longer-term studies (weeks).

In a paper he recently published in the Journal of Clinical Endocrinology and Metabolism, Blundell recently examined the effects of medium-term exercise on fasting and post-prandial levels of appetite-related hormones and subjective appetite sensations in overweight and obese individuals.

The study included 22 sedentary individuals who took part in a 12-wk supervised exercise programme (five times per week, 75% maximal heart rate) and were requested not to change their food intake during the study.

Not only did exercise result in a significant, albeit modest (~3 Kg), reduction in body weight and fasting insulin and an increase in ghrelin plasma levels but also in a reduction in fasting hunger sensations.

A significant reduction in postprandial insulin plasma levels and a tendency toward an increase in the delayed release of glucagon-like peptide-1 (90-180 min) and a greater suppression of postprandial ghrelin.

Thus, although exercise-induced weight loss was associated with physiological and biopsychological changes towards an increased drive to eat in the fasting state, this compensatory effect seems to be balanced by an improved satiety response to a meal and improved sensitivity of the appetite control system.

However, as Blundell pointed out, these mean changes hide the immense diversity between individuals.

Based on these studies it appears impossible to predict in advance how individuals will respond: Some people, in response to exercise, will be hungry and may overeat – others may find that they are much better in controlling their food intake.

Importantly, all subjects, irrespective of their body weight, showed a reduction in their amount of body fat and improvements in risk markers like physical fitness and blood pressure.

Thus, Blundell concludes, exercise does reduce body fat (even in people who do not lose weight) and has beneficial effects on important health parameters.

The answer therefore clearly is: no, exercise does not make you fat, but don’t expect to lose a lot of weight.

The many important benefits of exercise can, unfortunately, not be measured on a scale.

AMS
Edmonton, Alberta

Martins C, Kulseng B, King NA, Holst JJ, & Blundell JE (2010). The effects of exercise-induced weight loss on appetite-related peptides and motivation to eat. The Journal of clinical endocrinology and metabolism, 95 (4), 1609-16 PMID: 20150577

2 Comments

  1. I have been measuring pre and post exercise results with my patients for 20 years. Measuring weight without composition analysis is a set up for failure. Some people have more visceral fat vs femoral and subcute fat. There is so very little actual research in this area, its refreshing to see a few scientists realize the importance of evidence based research in exercise adaptation.

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  2. Excellent article Dr. Sharma…..
    Several studies have shown that the major benefit of weight loss is that it improves not just one risk factor but the entire risk-factor profile. Health benefits increase as weight loss moves along a scale from modest to considerable, but modest weight loss even so produces clinically significant benefits. Accordingly, Dr. Louis J. Aronne, MD, 2001, modest weight loss is appropriate initial therapy for obese patients with comorbid conditions. Maintaining a modest weight loss is more desirable than achieving a larger weight loss that will be regained. For example, a man who decreases his BMI from 40 kg/m2 to 38 kg/m2 (~5% weight loss) will theoretically decrease his mortality risk by 12%. Weight loss of 10% or less can improve the complications most commonly associated with obesity. This amount of weight reduction has been shown to improve glycemic control in obese patients with type 2 diabetes, reduce blood pressure in obese patients with hypertension, and improve lipid levels in obese patients with dyslipidemia. One such study, comprising 263 patients with type II diabetes or impaired glucose tolerance, correlated each average 1-kg (2.2-pound) weight loss with a 3-4 month survival increase. A 10-kg weight loss would restore the 35% loss of life expectancy associated with the diagnosis.Therefore, Hypertension is more likely to accompany obesity than normal weight, and weight loss appears to lower blood pressure as an independent effect. Although substantial (>10%) weight loss is unequivocally associated with lowered blood pressure, the effect is frequently reported with modest weight loss. Reducing weight in the patient with hypertension lessens obesity-associated increases in cardiac output, blood volume, and intracellular sodium. Benefits directly relate to the amount of weight lost. A 12-kg loss lowers blood pressure an average 21/13 mm Hg, even in patients with untreated hypertension.Health benefits of weight loss in patients have been studied extensively. Study after study has shown that most of those who attempt weight loss eventually regain the weight they lost. The primary goal and the major challenge for the patient and the doctor is to managing obese patients to improve their ability to sustain whatever weight loss can be accomplished. Whereas diet, exercise, and behavioral management are the bases of treatment, especially at this time when there is a lack of drugs for obesity. Medication and surgery can be considered in appropriate individuals. In the future, treatment of obesity could supplant the treatment of the many chronic diseases, such as diabetes, hypertension, and hyperlipidemia, which take up a large part of office practice today.

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