It almost never fails: 45 minutes into your morning swim workout and you feel the stomach pangs of hunger and the intervals become harder and harder to complete. Hunger strikes—and it’s a biological cue that your body needs fuel!
When you are running or cycling, you usually find you are not hungry, and after a hard run or ride most people feel like they have no appetite. But swimming? It’s a completely different story. Part of it has to do with the intensity of exercise: high intensity mutes your appetite while lower intensity triggers it. Although high-intensity work in the pool should mute your appetite, you might still find the hunger pangs are there. This is due, in part, to the fact that cold water seems to trigger a response which makes you hungrier compared to other endurance sports in which you burn the same amount of energy.
The reason for this appetite-stimulating effect of swimming is not completely understood. One possible reason relates to the suggested link between temperature (specifically body heat loss) and food intake. In colder temperatures, food intake may increase as a mechanism to generate body heat through diet-related thermogenesis. Thermogenesis is the body’s process of using energy to produce body heat. Even though swimming generates body heat due to the action of exercise, the immersion in the cool water leads to overall body heat loss. It is important to note heat loss in water is far greater than that in air, which means that in a room of 78°F the body can maintain its body temperature without any extra heat production. However, in 78°F water, the body needs to produce heat and burn extra energy to counteract the heat loss in water. Swimming in warmer water (83°F and above) has no effect on increasing hunger.
It is also possible that changes in brain signals and neurotransmitters (chemicals that carry messages between nerve cells) might be a factor in increasing appetite. This is plausible because there are specific regions of the brain linked to appetite and reward, and non-homeostatic factors (such as eating for pleasure or the motivation to eat certain foods over others) can also influence appetite and eating behavior.
So what should you do to mitigate the increased hunger? First, have something to eat before you hit the water, or if eating in the early hours of the morning is not something you can stomach (pun intended!), then have an electrolyte drink on the deck and consider some energy bites or energy chews if your session is going to be longer than 60 minutes. Having a protein bar or drink for the drive home will also help abate the hunger (protein is satiating). The acute effect of the increased hunger can also be mitigated by increasing your body temperature after swimming. This can be as simple as a short 20-minute jog, a few minutes in the sauna, or taking a hot shower, and/or drinking a hot drink.