May 3, 2021Physical Activity and Its Role in Appetite Regulation
Competitive athletes all have a common goal: to optimize performance and recovery. This happens through training to enhance technical skills and through physiological adaptation. Optimal performance, recovery, and physiological adaptation all have ties to nutrition, and similar to training, nutrition habits for top physical performance need a well-developed plan. Some goals of nutrition to support training and improve performance include:
- Adequate energy intake, both day-to-day and during exercise to support training demands and optimize performance
- Adequate protein intake for growth and repair of tissue
- Adequate carbohydrate replenishment
- Adequate hydration, both daily and during exercise
- Appropriate weight and body composition
- Intake of nutrients that support recovery
- Appropriate timing of nutrients
Hunger is an important signal that the body is in need of energy: this comes in the form of food or food supplements. There are inaccuracies in the body’s capacity for appetite regulation and hunger that can keep athletes from meeting the above-mentioned goals. Physical activity plays a large role in appetite regulation, though maybe not in the way you think.
Regulation of Appetite
Appetite and food intake are regulated by hormones that are secreted from the gut. Ghrelin, sometimes known as the “hunger hormone”, is what makes people want to eat. It is secreted in the fasted state and triggers the brain to release a neuropeptide, NPY, that is a strong stimulator of appetite. After food is consumed, the hormones PYY and GLP-1 are secreted from the gut to indicate fullness, causing the reverse effect of ghrelin. This “fullness” signal, however, is not precise in matching “calories-in, calories-out” for each bout of exercise. For example, if 600 calories were expended over a training session, the hunger and fullness signals are not precise enough to promote the consumption of exactly 600 calories. However, to match long-term energy intake vs energy expenditure, there are regulatory mechanisms in place to maintain body weight.
Leptin is an important hormone involved in long-term energy balance and weight maintenance and is produced by fat cells. In non-obese individuals, leptin’s secretion reflects the body’s stored energy state (fat) to help with energy balance. With excess energy intake over time, increased fat storage causes leptin levels to increase in an attempt to suppress appetite and reestablish “normal” body weight. In obese individuals, however, there seems to be a resistance to the action of leptin. Even though higher levels of leptin may be present, it does not result in decreased energy intake. Certain sports have athletes that are at a higher risk of being obese, such as football offensive lineman or throwers within track and field. It is important to be aware of this hormonal mismatch if helping an individual work toward weight loss. In athletes with chronically low energy intake, leptin levels are reduced and ghrelin levels are increased.
Exercise and Hunger Response
The ways the body regulates food intake and energy expenditure are complex, interrelated, and not completely understood. There is also an indication that these mechanisms can be altered and disrupted by physical activity and food consumption. Hormones that regulate appetite are particularly affected post-exercise by decreasing the feeling of hunger. This is important for athletes to consider, as consuming food within 30 minutes of physical activity helps to optimize recovery.
Perhaps surprisingly, Schubert et al. (2013) suggested that instead of promoting hunger, exercise decreases the hunger hormone ghrelin in the hours after exercise, causing suppression of hunger and a delayed drive for food and beverage intake. When blood flow is directed to the muscles and skin during physical activity, blood is not flowing to the gut to stimulate hunger. Exercise and training that cause larger metabolic demand and greater muscle damage tend to suppress hunger levels even more. These effects can be concerning for competitive athletes when considering the importance of nutrient timing on post-exercise recovery for training adaptations. Ingestion of high-quality proteins immediately to two hours post-exercise accelerates muscle protein synthesis; the anabolic effect of exercise diminishes with increasing time during recovery. Schubert et. al (2013) also indicated that over the next 2-10 hours post-exercise, individuals do not increase their food intake to match the energy expended. While taking advantage of this discrepancy may be an effective strategy for weight loss, for elite athletes trying to maintain or increase lean mass or optimize recovery, it can have a negative impact. Signs of under-fueling/recovery include:
- Decreased muscle strength
- Decreased carbohydrate stores
- Decreased endurance performance
- Increased injury risk
- Decreased training response
- Impaired judgment
- Decreased coordination
Combatting Exercise-Induced Changes to Appetite
There are a number of ways to overcome appetite suppression to ensure proper recovery. Tips that can help athletes optimize recovery post-workout include:
- Choose liquid forms of nutrition such as a balanced recovery shake to capitalize on the heightened thirst response vs relying on hunger.
- Choose a protein recovery drink with 20-30 grams of protein within the first 30 minutes, followed by a full meal within the next 90 minutes.
- Cool core body temperature with cold drinks, an ice bath, etc. to induce the return of hunger.
- Do not skip meals; this helps keep energy intake consistent day-to-day and keeps appetite-regulating hormones functioning properly
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Registered sports dietitians are uniquely qualified to assist athletes with individualized nutrition plans to ensure proper fueling for optimal performance and recovery. For assistance with strategies to combat appetite suppression, refer to a registered sports dietitian for an appropriate, individualized nutrition and recovery plan.
Written by a Collegiate and Professional Sports Dietitians Association Registered Dietitian (RD). To learn more about sports nutrition and CPSDA, go to www.sportsrd.org.