Headline or Headlie? Exercising while dieting is bad for bone health

Emma Brown - Nutritionist | 20 Sep, 2019

The media love to grab attention with a shocking headline – but how much can we trust? If we took every headline at face value, we'd be living in a world of confusion. In fact I imagine this is the case for a large section of the British public when it comes to the topic of health and nutrition! One day we're told something is good for us and the next day it's not!

So it's important to dig deeper into the story behind the headline and look at the research that sparked it. Often we discover the shocking statement is nothing more than just that – with little to substantiate it, and 'research' that raises more questions than provides answers.

This week, we're looking into this headline:

'Why women over 40 should NEVER diet and exercise at the same time'

A pretty concerning statement and sure to grab your attention if you're a 40+ female trying to lose weight and exercising regularly! But before you cancel your gym membership, let's look at where this headline came from.

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Source: https://www.womanandhome.com/health-and-wellbeing/diet-fitness/diet-exercise-bone-density-loss-332202/

What was the research?

A study conducted at The University of North Carolina on mice found a 30% reduction in calorie intake teamed with regular exercise for 6 weeks, lead to a 20% increased loss in the bone density of the mice.

What's right with it?

Randomised control studies in animals can help to highlight potential areas for further research in humans – so they are certainly useful. But to take the results of one small study in mice and immediately extrapolate the results to humans is irresponsible and misleading.

What's wrong with it?

There are many things to consider when establishing how robust the results of a study are. In the case of this research, there are a number of reasons why we shouldn't heed the advice straight away.

  1. The study used a small sample – just 7 mice in the calorie-restricted and exercised group. This doesn't make for hugely compelling findings.
  2. The study used mice – we can't directly translate the results to humans as we don't know if our bodies would respond the same way without repeating the experiment on humans.
  3. There has been some research on humans to suggest calorie restriction in general can lead to bone loss. However, other studies haven't found an increased effect of exercise on bone density reduction – plus countless studies have shown the benefit of exercise on bone health in humans.
  4. Allowing one study to fly in the face of many others that promote the benefits of diet and exercise is neither scientifically sound nor wise.

Take home

Regular exercise is hugely important for all of us, not just to aid weight loss (if that's your goal), but to help improve general health and fitness too. It builds and maintains lean muscle mass, leading to increased strength, stability and mobility. It also benefits cardiovascular health and our mental health. Even if it were the case that exercise and calorie restriction potentially reduced bone density, it could be argued that the other benefits of exercise and weight loss would far outweigh this potential downside – so it's important to look at it from all angles.

Any headline promoting a sedentary lifestyle given the current UK obesity crisis is extremely irresponsible and merits a much closer examination before dismissing the longstanding official health advice we've been given.

On the contrary....

There are sometimes headlines with a positive message we can take at face value! For example:

'A burst of exercise cannot be too short'

Advice from the Chief Medical Officer last month said we should not worry that only certain levels or durations of activity are worthwhile. In fact ANY amount of exercise does us some good. This is an positive message we can all take on board and be encouraged by. We're all for headlines like this!

Nutritionist Emma Brown (ANutr), MSc Human Nutrition is passionate about how food science applies to the human body, and how the nutrients in what we eat affect us and ultimately have an impact on our health.