by  Ed Loveday , Senior Trainer

by Ed Loveday, Senior Trainer

How having a better understanding of human biology and evolution can help you make sense of what’s going on with your body whilst dieting to low body fat levels.

You are a survival machine. Every process in your body is governed by your genes. Genes control what you do, you don’t control your genes. Your genes want to survive and be replicated in your offspring. If you die before reproducing, they can’t do this.

In a way then your genes could be described as having selfish but not sentient character traits which are all geared towards their own survival. It is because of this that the genes contained inside of you have survived this far, and given the right set of conditions can continue to replicate and exist for generations long after you are dead.

Ok so how does this relate to dieting?

Dieting to low body fat levels is difficult. But if you understand that the difficulty is down to your genes wanting you to live, survive and replicate then we can be better placed to understand the process and try and find a solution to the problem in order to keep fat loss progress going.

Let us examine some common problems that occur when dieting to low body fat levels.


1.  My body is holding on to fat / weight loss has stalled.

Weight loss has plateaued so you must reduce calories right? Maybe.

Being in a calorie deficit is essentially starving to death, albeit slowly. Now you may know that you are not going to actually starve to death but your genes don’t. So they will try their best to limit energy expenditure if they feel that energy intake is inadequate. This will translate into feeling tired and lethargic, an unconscious reduction in NEAT and a slowing of the metabolism as well as a lack of motivation to train etc.  This is bad for fat loss but good for your gene survival because it means you maintain your weight and halt the “starvation process”. You can counteract this process by setting a smaller deficit and dieting for longer rather than a severe deficit, not killing yourself with your training, experiment with refeeds or calorie cycling, ensuring sleep is adequate and keeping external stress to a minimum. This will hopefully convince your genes that you are in a safe enough situation to continue losing fat.


2.  I’ve lost my libido.

Hang on a second, genes want to replicate, that’s not going to happen if you don’t want sex right? Good thought process but let’s examine this a little more closely. Your genes want you to survive and replicate but they also want your offspring to survive. If food is scarce (dieting) then the last thing your genes want to happen is for you to have a baby and reproduce, this leaves another mouth to feed and could ultimately compromise the survival of both you and your offspring. I know what you’re thinking, “but there’s loads of food about and my baby won’t be dieting, and I’m using contraceptives so there won’t be a baby anyway”. Your genes again don’t know this, through most of human evolution food has been scarce, contraception hasn’t existed and it has been a useful tool for our survival for you to lose your libido in times of food scarcity.

OK, so how can we counteract lack of libido; this is a tough one, sex is great and we should all have more of it. If you are in a relationship talk about it with your partner so that it doesn’t become something that drives you apart. Ensure your calorie deficit is not too low and that sleep and vitamin/mineral levels are adequate. Ensure fat consumption is enough to maintain healthy hormonal processes and experiment with diet breaks. Don’t overthink it but understand the reasons behind your lack of libido are entirely normal rather than problematic.


3.  I store fat easily and lose fat slowly.

Surely if I get fat easily then I’m more likely to die?

Congratulations. You’ve just identified a trait that has allowed our species to survive through droughts and famines and times of severe cold weather but you’re disappointed that you possess these genes too? Genes that encouraged rapid fat loss and slow fat storage would have died out long ago as the people who possessed them would not have survived without food for as long as people who had the fat storage genes. How can we use this information to our advantage? Accept that fat loss is going to be a slow process and be aware that if you do overfeed then your body will store fat very quickly. It’s not unlucky, it’s advantageous, or at least was before super markets and central heating and not having to catch your own dinner.


4.  Why do I feel more stressed/Not getting enough sleep?

These are bad things to be happening so my genes can’t be working in my best interests by allowing this to happen can they? Yes.

By hard dieting you have created an environment in your body where it is in an unfed state and your body is unconsciously worrying about when your next meal is coming from. This will make cortisol (the stress hormone) levels rise which can lead to sugar cravings if left unchecked. By limiting sleep, your body spends more time awake which from an evolutionary standpoint allows more time for you to hunt for food. Having no food would have been a primary point of stress for early man. Although we now have various lifestyle and environmental factors that can cause us stress, your genes don’t know the difference between each individual stimulus so will respond similarly in any stressful scenario. These genes have been useful for our survival for generations and will likely continue to be.

So how can we use this information to help with the dieting process? Make sure you are not in too large a deficit, try and do things that are relaxing and that allow the body to rest and recover, ensure your diet is sufficient in carbohydrates and maybe experiment with eating carbs towards the end of the day.


Hopefully now you have a better understanding of why dieting is an uncomfortable process for your body to go through. You are trying to fight an instinctual process that has been successful in keeping humans alive since the dawn of our species. By appreciating this perhaps you can make the journey a little smoother and more collaborative with your physiology rather than against it.


The Selfish Gene – Richard Dawkins.

A Guide to Flexible Dieting – Lyle McDonald.