Thirty minutes exercise is enough to start losing weight

If weight loss is your goal, you may have been discouraged by the amount of exercise you might need to commit to in order to make a meaningful difference. It’s the sort if thing that can put you off your workout altogether if you’re not careful. Not any more. This research seems to indicate that 30 minutes of exercise is just as effective as 60 minutes in promoting weight loss.

In a sample of 60 heavy – but healthy – men over 13 weeks, half the group were set to exercise for 60 minutes a day wearing a heart rate monitor and a calorie counter, whereas the half of the group only exercised for 30 minutes per day. Both halves of the group had to exercise enough to raise a sweat.

On average, those who exercised for 30 minutes per day lost 3.6kg over the 13 weeks – the average weight loss in the 60 minutes per day exercise group was 2.7kg. Actual fat mass was reduced by similar amounts for both groups – approximately 4kg. A bonus for the 30 minute a day group was that they seemed to burn more calories than expected for the training programme that was set for them. Another key factor was that there did not seem to be any statistically significant changes found in energy intake or non-exercise physical activity that could explain the different responses between the 30 mins v 60 mins exercise per day groups.

A few explanations were put forward by the Danish researchers, though we can’t be certain about any of them. Amongst them, they suggest that perhaps 30 minutes of exercise felt so ‘doable’ that the participants had energy left over to start exercising more intensely within their 30 minute allocation per day.

A feature of this research is that it focuses on a group of moderately but not severely overweight men – a group that now makes up 40% of the Danish male population. It certainly adds data to the general evidence that 30 minutes of aerobic exercise on most days – even if you break that up into smaller chunks – is a worthwhile and beneficial goal to set yourself.

Does thinking that you are fat make you fat?

What we have suspected for some time – that constantly being bombarded with pictures of skinny people – may have a negative impact on our own thoughts, feelings and behaviour after all. Indeed, despite the images of super-thin bodies become omnipresent and infecting more and more of our waking moments, at a population level we are becoming more overweight and obese.

It looks like the kind of comparison that this ubiquitous imagery could encourage has a significant impact. Researchers at the Norwegian University of Science and Technology have found that normal weight teenagers who perceive themselves as fat are more likely to grow up to be fat. This is the first study to look at the relationship between perceived weight and actual weight in a longitudinal study of teenagers and young adults. 1196 normal range weight adolescents were followed up as young adults 11 years later. After controlling for covariates such as age, sex etc, adolescents who perceived themselves as overweight had a significantly larger weight gain into young adulthood that adolescents who perceived themselves as having a normal weight (0.66 BMI units; 3.46cm waist circumference). This was unrelated to levels of physical activity.

Thinking that you are fat as an adolescent – even when you are not – can lead to become significant fatter as an adult. 22% of girls rated themselves as overweight as teens, compared to 9% of boys – this might be due to media focus on body image focusing on girls – especially at the time that these young adults were teens. Worryingly, 59% of girls who felt fat as teens became overweight as adults. If we consider waist circumference, 78% of teens who initially perceived themselves as fat later became overweight as adults.

It’s difficult to know what causes the increase in weight, and it is likely to be complex. We know that stress can cause an increase in weight – the authors suggest that the psychosocial stress of not being your ideal body type (wherever that idea may come from), as well as thinking of yourself as overweight can lead to weight gain. Perhaps another explanation is that seeing yourself as fat can lead to skipping of meals – and we know that dropping breakfast has been linked to obesity through various mechanisms.

The lesson I take away from this is the importance of anchoring our self-perceptions of weight in fact, rather than glossy imagery that we come across every day. This is even more important in the crucial developmental years of adolescence, where we try to understand and balance the plethora of information telling us how we should be adults and how to be acceptable to ourselves and others. Challenging this information, and developing alternate pathways through healthy diet, exercise and mental wellbeing is so important, and is a set of skills that needs to be taught.

The key to managing your weight is eating less, not exercising more

New research in a hunter-gatherer community seems to indicate that managing what that you eat is more important than exercise in determining how much weight you gain (or lose).

A study into energetics and obesity in the Hazda people of Tanzania revealed that although physical activity levels were much higher for Hazda men and women than their western counterparts, once size and weight were taken into account their metabolic rates were pretty similar. This was something of a surprise, as most people would expect that Hazda people, and others living a hunter-gatherer lifestyle would burn many more calories than their more sedentary equivalents in more ‘developed’ societies. Energy expenditure looks more complex than a simple linear relationship. But what did become apparent was that although physical activity does seem important in keeping you healthy, it won’t keep the weight off. It looks like we need to stick to eating less to do that.

So, if you’re relying on your workout to give you permission to eat more, think again. If your goal is to lose weight, you’re probably not doing as well as you could be.