Diet and exercise are regarded as the most effective means to maintain weight as well as lose weight. But, there’s sometimes a catch as their effectiveness varies between individuals. Moreover, many people find it really difficult to keep the weight off. Researchers think this may happen in part because the body adapts to weight loss by increasing appetite and decreasing energy expenditure. Here is where exercise, in particular, is thought to help by counteracting these effects. Although, some reports have shown that exercise is not effective for weight loss in women as compared to men and it may even cause fat mass to increase (Sawyer et al., 2015).
Exercise is thought to help prevent weight gain by reducing the desire to eat…at least in males. A new study published in the American Journal of Physiology – Regulatory, Integrative and Comparative Physiology explored why the post-exercise eating response differs between male and female rats. Rats were divided into two groups and fed either a diet high in fat (46% kcal from fat) or a low fat diet (11.5% kcal from fat) for 6 weeks. Whereas the diet high in fat resulted in a positive energy balance and greater food intake for male rats, a similar effect was not observed in the females.
At the end of the diet, rats in each group were divided again into an exercise training group (treadmill) and sedentary rats. The researchers found that the exercising male rats ate less food (less calories in) and gained less weight compared to sedentary rats. They also ate less food on days they exercised compared to the days they rested during the exercise training program. In contrast, the female rats ate more food after exercise and gained the same amount of weight as sedentary rats. This was attributed to the exercising females consuming more meals than the sedentary females. In other words, it took longer for the exercising females to feel satiated. Just like the holidays, when the rats were presented with highly palatable foods, both male and female rats overconsumed whether they exercised or not.
Interestingly, exercise was found to actually decrease the satiety hormone leptin in exercising males whereas concentrations did not change in females. When the researchers gave the rats leptin, it suppressed appetite in all study animals. That means the animals were still sensitive to leptin even though concentrations were decreased in the male rats after exercise.
Other researchers have examined changes in leptin after exercise in Greyhounds vs sled dogs – both remarkable endurance athletes. Similar to the exercising male rats, leptin concentrations are low in these dogs before exercise compared to domestic breeds. It was thought that levels of leptin are lower as the athletic dogs had less fat compared to domestic dogs.
RM Foright, GC Johnson, D Kahn, CA Charleston, DM Presby, CA Bouchet, EA Wellberg, VD Sherk, MR Jackman, BN Greenwood, PS MacLean. Compensatory eating behaviors in male and female rats in response to exercise training. American Journal of Physiology – Regulatory, Integrative and Comparative Physiology. 319(2): R171-R183, 2020.
BJ Sawyer, DM Bhammer, S Angadi, DM Ryan, JR Ryder, EJ Sussman, FMW Bertmann, G Gaesser. Predictors of fat mass changes in response to aerobic exercise training in women. 29(2): 297-304, 2015.
MA Bell, CB Levine, RL Downey, C Griffitts, S Mann, CW Frye, JJ Wakshlag. Influence of endurance and sprinting exercise on plasma adiponectin, leptin and irisin concentrations in racing Greyhounds and sled dogs. Australian Veterinary Journal. 94(5): 154-159,2016.