What if I cut my energy intake by 50%? Weight loss resistance

by | Feb 19, 2023 | Nutrition

This conversation started on Facebook. Peter, a runner, asked what would happen if he cut his energy intake in half!

During the conversation, you will find out that even when losing weight it is not always good to start with a caloric deficit and the consequences of low caloric intake on the athlete’s appearance and performance.

If at 17,600 kJ per day, my weight is stable below 65 kg, how much would I weigh with half the intake?

A theoretical question? The weight would go down rapidly and, for the most part, the muscle mass as well. Subsequently, compensation by overeating would probably occur due to the increased feeling of hunger. So the typical yo-yo effect

This is really theoretical, but I wonder if the metabolism would also go down and I would be more cold and so on, and possibly if I would be more tired and run less.

If you wanted to keep the ~2200kcal intake, your body would adapt. Below a certain limit, you would no longer lose weight, but your overall physical activity would decrease, your sleep would worsen, your performance would decrease over time, you would often be cold, I assume your bone mineral density would decrease, and soon you would get stress fractures.

Simply put, the body would borrow energy for running from other systems – that is thermoregulation, the reproductive system, and tissues including muscles, tendons, and bones…

Daniel, thanks for the great comments. If I may have a question on this topic. If Petr is weight-stable at some intake, he has a stable number of km and a certain stable number of kcal per month, i.e. approx. 4200 kcal for him. Is there any possibility, for a person who eats too little, either downward or upward, how to find the optimum? Is it clear in Peter’s case that he is at his optimum and that he should not reduce his intake any more? Maintain his intake and let it be? And on the contrary, if it is probably too little for someone (see the examples you mention), how to proceed correctly, how to reasonably increase and what’s the point when we can say – this is the point when the intake is appropriate. Thank you very much


In most cases, we can start from the table values for TDEE (total daily energy expenditure including basal metabolism and activity).
If I see that an athlete’s measured energy intake is significantly lower than what the table values show, I look deeper:

  • Are you cold more often?
  • Do you often have sweet cravings?
  • How often do you get injured?
  • What’s your libido?
  • How well do you regenerate?
  • Are you less motivated to train?

Clinically, an intake lower than 45 kcal/kg is currently reported as a relative energy deficit for women, below which female athletes should not go. On the contrary, people notice too high energy intake simply – by gaining weight.

The search for the optimum is based on observation. From my point of view, the optimal energy intake for performance is often higher than athletes are willing to intake. This is more for those elite or performance athletes.

In my opinion, for the general sports population, the optimum is a sufficiently large energy intake for high-quality sports and life, which is also mainly sustainable for the individual in the long term. So, on paper, an athlete may be a little lower than optimal, but at the same time the athlete is not malnourished, they feel good, and do not experience the negative effects.

Does it make sense that way?

I think that in the opposite case, there will probably be some weight gain first – short-term and gradually the body will get used to it. Btw. I now have an example of a German runner, if you haven’t noticed, interesting to read, but it’s a very extreme example, in my opinion. It probably won’t be so striking for most athletes – performance athletes.

I’m in contact with Tanja’s trainer🙂 It’s not such an extreme example either. It was about the fact that the 1500 kcal was too low for Tanja, which we often see, especially in sportswomen. These are the symptoms we mentioned before.
“I think that in the opposite case, there will probably be some weight gain first – short-term and gradually the body will get used to it.” this can be water, glycogen, but also muscle mass.

But you probably have in mind the case when a person is on a low caloric intake for a long time and then increases it, like Tanja. In that case, weight gain can be part of the process. Anyway, the body’s ability to adapt metabolism “upwards” is very limited compared to “downwards”. From the survival perspective, the body always wants to store energy for the worse times, and it senses we are starving, it tries to reduce the energy expenditure as much as possible for survival.

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