Why am I SO hungry?
“I don’t know what it is but I often feel more hungry on days when I’m not training – why is that?”
It would seem logical that exercise is associated with increased energy expenditure and therefore increased hunger and drive to eat, so why is it that we often feel extra hungry on days off training?
Firstly, let’s revisit some basics of metabolic physiology. Several factors contribute to your hunger levels, not just the amount of activity that you do. There are a number of major players in appetite regulation including:
- Your body composition (especially muscle mass)
- Resting metabolic rate
- Gastric response to ingested food
- Changes in appetite hormones (e.g. insulin, ghrelin, cholecystokinin, glucagon-like peptide-1 and Peptide YY, leptin)
Here are some possible explanations to consider why we feel hungrier on rest days.
Hunger hormones and exercise
There is evidence that exercise influences all of these components. For example, during times of energy deficit (e.g. the day after a big training day), our appetite hormones are signalling for us to eat more, and this may contribute to increased hunger levels.
On days of high training load/volume, hunger is often suppressed after exercise (especially after vigorous exercise), most likely due to redistribution of blood flow to the extremities, away from the gastrointestinal tract.
There appears to be a delayed compensatory response, whereby a lag of 1-2 days, or longer, seems apparent in order to ‘even out’ days of high(er) energy expenditure. Interestingly, some people are compensators and others not. That is, some eat habitually (the same thing which doesn’t change from day to day) while others eat according to hunger and/or based on the activity completed (or not).
Physical activity may improve the sensitivity of satiety signalling systems to eat
The theory (called the ‘glycogenostatis theory’) suggests that glycogen availability has a central role in feedback signals to the body to restore energy balance. After glycogen depletion (which occurs during exercise), one of the body’s priorities is to restore carbohydrate levels in the body. This theory suggests that after exercise the glycogen depletion of the muscles exerts a signal to the body to trigger compensatory eating, which in turn, restocks carbohydrate in the body. The specifics of this signalling pathway are currently relatively unknown and further research is required to fully understand the mechanisms involved.
Physical activity could alter macronutrient preferences and food choices
Another prominent theory suggests that there is a biological drive to seek particular foods to replenish blood sugars or glycogen. This effect could also relate to preferences for particular tastes associated with certain nutrients (e.g. sweetness which is often associated with carbohydrate rich foods).
Catching up for missed time
Some research says that often people don’t always feel hungrier in the couple of days following a bout of exercise, but do feel hungry if they have missed a meal. Translate this to real life and we have the scenario where training may replace time spent eating food, which then leads to an increase in appetite and drive to eat in the days afterwards.