As we strive to determine where our body weight should sit, how we achieve and maintain weight loss and what control we ultimately have over that, let’s start by being clear about what we know.

The role of genetics in weight

Various studies have concluded that our weight is 70% determined by our genetics. And this is backed up most convincingly, by identical twins reared apart. So, this suggests there is a small weight range across which our genetics determines we will sit. A bit like your height or shoe size, it’s part of the blueprint we’re born with.

We know there are hundreds of genes involved in body weight regulation. These influence a number of things:

  • Food selection
  • Food intake and portion size
  • How your food is absorbed
  • How your food is metabolised
  • How your energy is used.

The added dimension, of course, is our weight regulation has something to do with our food intake which is part of our environment. So now let’s consider what happens once our genetics begin interacting with our environment.

The interplay between our genes and our environment

We know our environment plays a part in how those genes are expressed. This is called epigenetics. So, this is things like:

  • Social status
  • Access to food
  • Availability of different foods
  • Levels of stress the body is subjected to
  • Sleep patterns
  • Gut microbiome

…influence how our genes are up regulated / down regulated and ultimate control how we function.

So, we’ve got our weight being driven 70% by our genetics and 30% by our environment. When we think about the environment we have these days, it’s a little different from our ancestry. It’s thought over time we have undergone genetic drift. In other words, it has suited our survival to have the ability to store reserves, but whichever way you look at it, we’re not biologically geared up for an environment that has a plentiful supply of food available to us 24/7.

Within the realities of modern-day life, some of us fair better than others when it comes to how our genes interact with it.
As an example, those in smaller bodies fed beyond the point of fullness, show reduced neuronal responses on a brain scan when presented with pictures of foods. Those in larger bodies do not show this reduced brain response and signals remained the same. Hence they are still stimulated by the presence of food. This is just one example of the influence of our genes and why there may be different responses to an ‘all you can eat’ buffet.

So, with all these variables in mind, now let’s look at some of the maths that weight loss science relies upon

Body Mass Index (BMI)

BMI is a crude measure first created in the 1940s based on population data of white males. Taking one measure of their weight across their adult life and then charting their age of death, it was designed to give an idea of risk at a population level. It doesn’t take into account age or body composition and was never supposed to be used as a measure of individual health risk.

It might also strike you that with all the complexities of the human body, it is ridiculous to think we all fit into neat little categories and exact cut-offs rounded up to a 5 or a 0. This was created because it was neat, not because it was clinically meaningful. The titles of the categories denoted by the cut offs have also changed over time, and have come to represent assumptions about health, purely because of the words used and what they have come to mean, for example, obese.
BMI gives some indication of risk in very crude terms, but its oversimplification is its downfall and has fuelled fat shaming and misinterpretation of health risk.

Calculating Basal Metabolic Rate (BMR)

Calculations are used to estimate how many calories you need at rest for all the body processes essential to life. This number can then be multiplied by an estimated activity factor to give your total energy need for the day. From this you can then theoretically hack around 500 calories out to achieve an energy deficit which should then bring about weight loss.
The challenge with banking everything on this is it’s an estimate – it doesn’t take into consideration any of what we’ve already discussed, nor the impacts on your physiology of previous dieting attempts which we’ll come to in a min. It uses your height, age and sex. That’s it.

To accurately know metabolic rate, you’d have to be in a lab with a chamber over your head. You’d need to measure your oxygen and carbon dioxide usage too.

Never-the-less we hang onto these equations because they sound convincing, and we’ve done some maths so it must be good. And we head off with a calorie target in mind that should ensure our weight loss success.

Assessing the calories we’re eating

Remember what I said about genetics, how we use those calories is not the same for everyone. We also don’t know how many of those calories are available to the body to use as it takes different amounts of energy to access them. For example, about 30% of the calorie value of protein is used to break that protein down. Therefore we’re not making use of all of the protein calories within a food.

But counting calories works, right?

Despite all the guestimates, yes it does, for a bit. And for how long depends to a certain extent, on how many diets you’ve done before. So, what’s going on there?

If we have repeated attempts at under fuelling, the body has to compensate for this as it tries to restore equilibrium. It creates what’s called a hyperphagic response, whereby it pushes us to over consume to compensate for the shortage. We also actively drive down our resting energy expenditure (BMR). And the next time we diet, the body remembers and launches into action, making each diet harder and harder.

How dieting messes with your head

Then we have the psychological components. The little chimp that comes out to play when we diet creating the ‘what the hell affect’ and the ‘last supper affect’. Dieting also makes us preoccupied and more anxious around food, which in turn makes us turn to food. Dieting also screws with our exercise relationship, a behaviour that completely independently of weight, is known to improve health and reduce health risk.

Is the NHS app worth downloading?

When the NHS weight loss app refers to exercise as a way to burn calories, it rather depressingly validates the connection between dieting and exercise. When the diet inevitably fails, it is common for exercise habits to trail off. We’re then left feeling deflated and demotivated. If we’ve been using exercise as a form of punishment for our so called ‘bad’ food choices, it’s also no wonder we don’t have a very positive relationship with it.

Apps like the NHS weight loss one, rely on equations that are fraught with nuance and challenges. They also continue to support the belief you can pick your dream or goal weight, and if you don’t achieve it, that’s a personality flaw. We can see from our physiology that it’s much more complex than that. Unfortunately attaching morality to our weight loss battles only serves to lower self-esteem. It increases weight stigma and worsens our relationship with food. It certainly doesn’t empower us to move our bodies and nourish them in a way that feels good. Even more so when we’re carrying around blankets of self-loathing every day.

Our weight regulation is controlled by the brain, in a region known as the hypothalamus. Unfortunately, it’s not ethical or legal to go poking around in there to figure out what’s really going on. For now, I think it would make a huge difference to acknowledge its complexity. To hold our hands up and say if you’ve dieted many times before and it didn’t work, this app probably won’t make any difference. That physical and mental health stand a better chance of improving if you take weight off the table as the focal lens through which you’re judging everything.

I’m not anti-weight loss but I’m tired of it being made to be so simplistic. Wise up NHS. Remember the guy who first realised washing hands was saving lives. He was laughed out the room – things we can’t even see causing death, no way! Now look what we know! I think it’s time we did the same for our body weight.

In my corner of the world, I’m trying to do just that – see details of workshops and courses designed to improve your relationship with food and support you to feel healthier.