A diet is just what you eat. But of course, when we talk about being ‘on a diet’ we are usually saying we are in a ‘calorie deficit’ i.e. losing weight by eating fewer calories than we burn.
You will often hear people say that if you stay on a diet too long or if your calorie deficit is too big you will go into ‘starvation mode’ and not lose weight. But is this true?! Yes and no!!
If you ate nothing you would waste away and eventually die i.e. you would starve to death. So there is clearly not a ‘starvation mode’ that can put a total stop on weight loss. But it does seem that reducing calorie intake by a sizeable chunk on a diet does result in your body burning fewer calories (beyond the amount that can be explained by the fact you are now carting round less excess bodyweight each day, and so burning less calories doing this) … meaning that your calorie deficit and so weight loss might not be as big as it ‘should’ be.
This phenomenon is more accurately called ‘metabolic adaptation’, rather than ‘starvation mode’. And it was probably vital for survival in ancient times when famine or inability to find prey continued for extended periods. In today’s western society of overabundance this is not so much a concern … but how are our bodies expected to know this when for millennia it was not the case!!
So what happens in ‘metabolic adaptation’. We don’t 100% know, but it seems we stop doing non-essential things like fidgeting, don’t maintain full working order of our reproductive systems (think low testosterone in men, absent menstrual cycles in women and less desire in both!) and cut back on keeping things like our immune system in tip top working order (hence people on extreme diets often get sick!). This all serves to save energy. We also seem to become more efficient at using food, meaning we manage to extract more energy from less food.
As well as metabolic adaptation, if you put yourself in too big a calorie deficit you simply can’t train as hard. Which means you will burn fewer calories – exercise activity can contribute as much as 10-30% of total calories burned per day in active individuals, so you can see how this can also start to hinder weight loss.
Is there a way to overcome metabolic adaptation? There is evidence that occasional refeeds (often known as ‘cheat meals’) or diet breaks (longer periods of taking in more calories) so that you take in slightly more calories than you would to maintain bodyweight may help reset metabolism. But the effectiveness of this is going to vary from individual to individual, how much weight you lose, and how much you cut calories by.
How do you know if you have gone too far by cutting calories too much? The first indications may be fatigue, trouble sleeping, declining performance in the gym, excessive hunger, and frequent illness. This is where you don’t want your body to get to – and the occasional refeed or diet break is not enough if you are doing this in between! In this case most people will need to increase their day to day calorie intake. And potentially still have some refeeds and diet breaks in there too. But again, it really does depend. Chat to a sports nutritionist to understand more and estimate a calorie deficit and diet approach that might work for you!