Exercise & Breast Cancer

Found this post from when I was working on this. It is a brilliant example of how complex  cancer is and I hope it stands to prove the over simplification at best and extremely dangerous at worst of claims like ‘ketones can help your cancer’..

Exercise and breast cancer: the effect on the tumor

This data is from animal models of breast cancer expressing triple negative tumors which are the most aggressive, hardest to treat and have the poorest outcomes. 

Before anyone says ‘it isn’t relevant because we are not mice’ .. yes there are limitations however;

– Animal models provide a tool to examine the effects of exercise on tumors in a closed experimental environment in which the lifestyle of the animal as well as the type and intensity of exercise can be controlled. This is not possible in the real world.

– Individuals with breast cancer display huge heterogeneity (they are all different) not just in terms of individual differences in health, age and ethnicity but in relation to their breast cancer type and treatment. This is less of an issue in genetically engineered mice models.

– Animal models also allow us to watch the tumors grow and thus make possible the detailed study of stage-specific responses to exercise. This gives us a greater insight into the development of tumors in relation to exercise and may help to identify the optimal mode, intensity and duration of exercise. 

In conclusion, some of the huge limitations in exercise science – namely sample size, heterogeneity of populations and lack of control can be overcome using animal models. We need to piece the information we get from human and animal studies together to give us the most comprehensive understanding.

On to what animal models can show us about the effect of exercise on breast cancer tumors..

– A reduction in tumor progression. Both the number of tumors and the size of tumors were reduced with exercise. 

– This reduction is thought to be linked to a reduction in inflammation (MCP-1 and IL-6 were both reduced)

– Intensity matters! – the reduction in tumor progression is generally seen in studies that have opted for exercise intensities of about 70% VO2 max. Interestingly, studies that have opted for low intensity exercise have found varying results with some even showing an increase in tumor progression. 

– The age of initiation of exercise (probably in relation to tumor status) may be of importance. Two very similar studies were carried out on a genetic mouse model where one study found a positive effect of exercise and the other found a slight negative effect. One of the key differences is that the positive effect was found when mice began exercise at a much younger age and the negative effect was observed when mice began exercising later in life. This may have implications for the age at which we encourage girls to start routinely exercising.

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This last point especially shows the complexity of cancer and how all tumors act differently & actually how even the same tutor can respond differently to a stimulus at a different stage in its life.

Losing more weight doesn’t mean losing more fat

Why fast weight loss isn’t impressive: It’s not (all) fat.


Going through check ins this week a few people seem disappointed with 1-2lb weight loss a week..THAT IS PERFECT!! Which begs the question are your expectations of rate of fat loss realistic?


Faster fat loss probably isn’t more fat.. here is why..

Many of you may have heard that 1lb a week of weight loss is optimal because which 1lb of fat is 3500 calories and this equates to a deficit of 500 calories a day for a week. Cool.


However, the 3500 calorie rule doesn’t quite add up when we look at real world weight loss. It might if you lost weight solely from fat but that is extremely unlikely and even more so in the first week or so of a diet where we often see bigger drops in weight (remember weight loss doesn’t = fat loss).


This is because we use energy from glycogen and muscle breakdown as well as from fat when we are in an energy deficit.


The energy balance equation does not directly refer to weight or weight loss. It refers to energy stores.


Energy balance is the difference between how much energy you take in and how much energy you expend –  over time this indicates how much energy you have stored in your body. This energy can be stored as glycogen in the muscle, as muscle tissue itself or, as fat.

So ,when you are losing weight it is coming from a mixture of glycogen, muscle and fat.. oh and all the fluctuations due to water retention & food volume.

Rapid weight loss can often mean you are losing a higher % of lean body mass and/or water. That’s why you’ll actually lose more weight if you don’t resistance train as you will lose more muscle mass.. just to be clear here.. MORE WEIGHT.. NOT MORE FAT!!!


So, you may weigh less but you will have a higher body fat % and you (arguably) won’t look as good.. unless you were going for the skinny fat look.. each to their own.


If you want to learn how to optimise your fat loss while minimising loss of lean body mass then get in touch.