Last month one of my blogs focused on the evidence which shows that exercise is, generally speaking, really quite ineffective for the purposes of weight loss. That is not to say that there’s nothing to be said for exercise. It is, for example, linked with a reduced risk of chronic and potentially fatal conditions such as cardiovascular disease and type 2 diabetes. Regular activity is also linked to enhanced longevity, . have benefits for the brain. As I concluded last month’s blog post, there are plenty of good reasons to exercise, it’s just that weight loss isn’t one of them.
The notion that exercise might have benefits for health, even in the absence of weight loss, was reinforced by a study published in the journal Obesity . In this study, 29 children and adolescents (average age 15) were put on a programme of exercise over a 12-week period. The study subjects exercised for 30 minutes, four times a week at 70 per cent maximum capacity (this would equate to a heart rate of about 140). About half the study participants were obese at the start of the study, while the rest were ‘lean’.
The study participants were assessed for a number of parameters, including fitness, fat levels in the muscles and liver, and insulin sensitivity (the ability for insulin to do its job). The exercise intervention did not lead to weight loss. Lean individuals did not see any significant benefit in the parameters listed above apart from fitness. However, for obese individuals, the story was different. Here, changes included:
1. reduced fat levels in the liver
2. reduced levels of insulin in the fasting state
3. improved insulin sensitivity
These changes, particularly in conjunction with enhanced fitness, would be generally taken signs of an improved metabolic state likely to translate into a reduced risk of chronic diseases such as cardiovascular disease and type 2 diabetes.
This study shows how it is possible for exercise to bring benefits for the body, even in the absence of weight loss. However, in this study, short-term metabolic benefits appeared to be confined to obese, rather than lean, individuals.
1. van der Heijden GJ, et al. Hepatic Fat Accumulation and Insulin Resistance in Obese, Hispanic Adolescents. Obesity 20th August 2009 [epub ahead of print publication]
There’s substantial evidence that growing muscle (lifting) improves glucose disposition, and using the muscle translocates glucose transporters to the cell walls ready for action – both ways of reducing insulin resistance, which appears to be backed by this paper. Presumably the non-obese children had no (or less) IR.
Of course one confounder is that is you lose fat and grow muscle you may not appear to lose that much weight. Long term though, reduced IR leads to reduced insulin levels which should make fat deposition harder – so long as you don’t exercise so hard you need to go face down in the carbs! Did they bother to tell you what they were eating?
In my experience working with those who have some degree of insulin resistance, it generally seems to take about 12 weeks to get control over the IR & return to some form of normal metabolic function. Once this point has been reached, then you start to see a degree of weight loss (providing all other contributing factors are also being managed). So positive study but perhaps just not quite long enough to see anything significant regarding weight loss.
Interesting. My 13-year-old has recently been able to resume competitive sport after 2 years off following a series of leg operations. During his inactivity he put on quite a lot of weight (not surprisingly), and that weight has now all come off again. Anecdotally, I am presuming that what has happened is that he has returned to his ‘natural’ (for want of a better word) size and shape, in which case I am also assuming he won’t go on losing weight however much more he trains (currently about 12 hours a week).
He is also T1 so obviously his insulin requirements are less on the days he does more sport (though by the bye acute mental activity lowers his blood sugar readings as much as physical activity), though his blood sugars can show an initial spike before dropping.
Love to hear more about this from anybody…