Hunger and appetite

People primarily eat for two main reasons: hunger and appetite. Linia Patel explores the difference.

Hunger is the need for food – an evolutionary protective mechanism that makes sure our body gets the fuel it needs to function well. Appetite, on the other hand, is the desire for food. It is a sensory or psychological reaction (“looks good”, “smells good”) that then stimulates an involuntary physiological and conditioned response to food.

Hunger hormones

The two most famous hormones involved in regulating hunger and satiety are ghrelin and leptin. Ghrelin is secreted primarily by the stomach when you are hungry. In the first animal-based studies, injecting ghrelin into animals would make them elicit food-seeking behaviour¹. In human studies, people who were injected with ghrelin would report feeling hungry even when they were full². Leptin, in contrast, is secreted from fatty tissues and acts as a satiety signal. Basically, leptin is an appetite suppressor that tells your brain that you can stop looking for food as you are full now¹. Animals and humans lacking the leptin gene develop morbid obesity as they just keep eating and eating^1,2.

Both hormones respond to how well-fed you are; leptin usually also correlates to fat mass — the more fat you have, the more leptin you produce. Some researchers think that leptin helps to regulate ghrelin. However, it’s now recognised that metabolic endocrinology is actually more complex than once thought and involves many hormones than just ghrelin and leptin^1,2,3. These hormones and their signals can get messed up especially with obesity⁴. Levels of hormones and our response to them depend on many factors, such as what you eat, your sleep patterns, your gut health and your innate level of mindful eating^3,4,5.

How to control hunger hormones

Looking primarily at improving levels of ghrelin and leptin, some studies have shown that consuming sufficient omega-3 fatty acids may help. In studies that included overweight and obese participants who consumed more oily fish or took omega-3 supplements, these participants were found to have an increased level of the fullness hormone leptin⁵. However, a lot more research is needed to understand fully the level of omega-3 needed and its application for people who are lean or normal weight too. Getting enough good-quality sleep has also been shown to reduce hunger⁵. Studies show that too little sleep can decrease levels of some fullness hormones by up to 26%. In a recent study including young men, sleep deprivation was associated with an increase in ghrelin levels, appetite and hunger compared with when they slept for 10 hours a night⁴.

In general, when looking at nutrients that influence the release of the fullness hormones, wholegrains (fibre) and protein have been shown to be the key. A high fibre intake means that you are fuller for longer, which helps manage your appetite in the long term. However, another key feature of fibre is that bacteria in your bowel ‘ferment’ fibre. Short chain fatty acids produced as a by-product of the fermentation process are thought to further promote feelings of fullness. A recent review reports that adding fibre-rich beans, peas, chickpeas and lentils to your meal can increase feelings of fullness by 31% compared to equivalent meals that aren’t based on beans. Diets high in refined carbohydrates in particular have been shown to increase levels of ghrelin³.

Under normal conditions, your brain is able to pick up clear signals of when you are hungry and full. However, eating quickly or while you’re distracted can make it more difficult for your brain to recognise these signals. Research has shown that mindfulness during meals can help people solve this problem by eliminating distractions and focusing on the foods in front of them⁵.

Hunger and fullness are two important and natural signals, which should not be ignored. Here are a few simple tips to help you along the way:

1. Add lean protein to each meal and snack.

   Protein at each meal will likely decrease hunger and may prevent you from overeating at your next meal.

2. Make friends with fibre.

   Eating a fibre-rich diet can decrease hunger and help you eat fewer calories. Eat more vegetables, fruit, wholegrains and beans and pulses.

3. Become a fish fan.

   Omega-3, particularly those found in fish and algae oils, have the ability to increase levels of the fullness hormone leptin. Eat fish (including salmon, mackerel, pilchards and trout) at least twice a week or consider taking a good-quality fish oil supplement.

4. Be mindful.

   Eating mindfully has been shown to decrease hunger and increase feelings of fullness. Using a hunger scale is one mindful way to tell the difference between true, physical hunger and hunger that’s really just in your head. Psychological hunger is a desire to eat that is caused by emotions like stress, boredom, sadness or happiness.

5. Sleep enough.

   Getting at least seven hours of sleep per night is likely to reduce your hunger levels throughout the day.

References

1. Austin et al. 2018. Hormonal Regulators of Appetite. International Journal of Paediatric Endocrinology Volume 2009.
2. Klok et al 2007. The role of leptin and Ghrelin in the regulation of food intake and body weight in humans: a review. Obes Rev. 8(1).
3. Patruno et al 2018. The relationship between leptin/ghrelin ratio and meals with various macronutrient contents in men with different nutritional status, A randomised crossover study. Nutritional Journal. Vol 17. 118
4. Miller 6. 2017. Appetite Regulation: Hormones, Peptides and Neurotransmitter and their role in Obesity. American Journal of Lifestyle Medicine. 13 (6)
5. Buss et al. 2014. Associations of ghrelin with eating behaviours, stress, metabolic factors, and telomere length among overweight and obese women: Preliminary evidence of attenuated ghrelin effects in obesity. Appetite. 76:84-94

About the author

Linia Patel has a BSc degree in biochemistry and physiology. Since graduating in 2006, Linia has become a leading dietitian and sports nutritionist. She is currently a PhD candidate in public health. Her passion is translating nutritional science into easy-to-digest and practical advice. @liniapatelnutiriton