Physiological systems that regulate appetite
Author: Paul Hollinrake, Researcher & Trainer in Public Health/5 July 2018
In a previous blog, we discussed the limitations of counting calories and highlighted that calories are not independent of each other e.g. reducing calories (energy in) can also result in a drop in metabolic rate (calories out). The human body is not a simple system where calories can be added or subtracted. We are a complex interplay of chemicals that co-ordinate food intake, desire to eat and all the food associations.
In this blog, some of the key physiological systems that regulate appetite will be discussed, which by definition is our desire to eat. This is different from hunger, which is our physical need to eat. Consuming food we crave is not just a product of physiology. But also how we interact with food in our environment (psychology of eating). This will be discussed in a future blog in this mini-series on appetite control.
The Neuro-endocrine System
The two systems that control appetite are the endocrine (hormone) and the neural system (nerves). Most people do not realise that the gastrointestinal tract (your gut) is the key organ for hormone production. Hormones can be classed as short and long-term. They respond to changes in the body to maintain homeostasis (keeping the body in balance). Also, they have many functions ranging from neurotransmitters, anabolic storage and sex hormones. Some of the key hormones responsible for appetite and energy balance along with their function can be seen in table 1.
The nervous system and neurotransmitters (hormone chemicals) are responsible for controlling smooth muscles and organs of the body. This is so that food can be moved and mixed in the digestive system. The enteric nervous system is the specialised network of nerves that are responsible for these actions and is often called the “mini-brain”. Some of the key neurotransmitters and their function can be seen in table 2.
Table 1. Hormones and appetite
|Ghrelin||Released from the stomach, pancreas, pituitary and hypothalamus, it stimulates growth hormone to encourage eating and regulates energy balance.|
|Insulin||Influences fat storage and burning and has been shown to increase appetite.|
|Leptin||Having a low leptin level results in a slower metabolism and the drive to in increase food consumption.|
|PYY||Released after a meal, to help suppress appetite, this hormone is released by the gut.|
Other influential hormones:
|Calcitonin, Amylin, GLP-1, Gastrin
Secretin, Cholecystokinin (CCK)
Gastric inhibitory polypeptide (GIP
Table 2. Neurotransmitters and appetite
|Endocannabinoids||Responsible for glucose and insulin metabolism in muscle and fat cells. Can drive hunger when food intake is low or an imbalance between omega 6 and 3.|
|Adrenaline||Impairs digestion during periods of stress|
|Neuropeptide Y (NPY)||Works in conjunction with Leptin to stimulate hunger while discouraging physical activity when food intake or body fat is low.|
|Serotonin||Released following a meal it regulates: anger, temperature, mood, sleep, appetite and vomiting.|
|Other influential neurotransmitters:||Gamma-aminobutyric acid (GABA)
Nitric oxide and Substance P
Vasoactive intestinal peptide (VIP)
Other appetite influences
Do you consider the effects of exercise/physical activity on your appetite? Well you should. Research shows that being active has an important role in appetite regulation. The body adapts to exercise very quickly and can become efficient at using body fat for energy and this helps to regulate appetite. Those who are not physically active tend to use more carbohydrate. Also, they tend to have more appetite swings because of varying blood glucose levels.
As already highlighted, key hormones such as leptin, ghrelin, insulin and PYY have a role in hunger and fat loss. However, exercise can moderate levels of these hormones. The hormone PYY has been shown to increase with exercise. This appears to be more the case with activities such as walking, jogging and cycling, as opposed to high-intensity exercise. Moderate to intense exercise seems to temporarily suppress your appetite.
The hormone estrogen can also drive hunger if levels are low. During the menstrual cycle women tend to eat more during the luteal phase (premenstrual cycle) when compared to the follicular phase. Older adults tend to have less of an appetite because of sex-hormone balance and nervous system signalling. It also appears that overweight individuals tend to have vitamin and mineral deficiencies compared to leaner individuals which can also drive hunger.
Summary and the real diet story
Within the X-PERT education programmes, we explain why trying to lose weight by the typical, eat less move more mantra can leave most individuals frustrated. They experience a weight plateau and the constant battle of feeling hungry. Eating food to provide the body with essential nutrients and energy involves more than just motivation and calorie counting.
Processed food and a lifestyle that includes too much chronic stress, lack of sleep and exercise can have a negative influence on appetite balance.
This blog has highlighted some key physiological systems that regulate appetite. Part 2 will discuss the influence of our environment on appetite and coping strategies we can incorporate to better equip ourselves.
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Key references and further reading
Chaudhri OB, et al. Gastrointestinal satiety signals. Int J Obesity 2008;32:S28-S31.
Chaudhri OB, et al. Gastrointestinal satiety signals. Annu Rev Physiol 2008;70:239-255.
Garcia OP, et al. Impact of micronutrient deficiencies on obesity. Nut Rev 2009;67:559-572.
Hagobian RA & Braun B. Physical activity and hormonal regulation of appetite: sex differences and weight control.Exerc Sport Sci Rev 2010:38:25-30.
MacLean PS, et al. Regular exercise attenuates the metabolic drive to regain weight after long-term weight loss. Am J Physiol Regul Integr Comp Physiol 2009;297:R793-R802.
Essentials of Sport & Exercise Nutrition, Precision Nutrition
What causes increased appetite – https://www.healthline.com/symptom/increased-appetite