While young people can eat anything that comes their way, older people often lose their appetite. To stay healthy at any age, it is important to know the reasons behind this.
“Our body more or less tells us what and when to eat, and maybe we should listen to it,” says Susanne Klaus, one of the leading researchers at the German Institute of Human Nutrition.
That’s logical. But the way our body demands energy from us varies throughout our lives.
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From being spoon fed by our parents as a toddler, to sneaking candy as a child, to eating everything we can get our hands on as a teenager, and then snacking on small, plain plates later in life, our appetites change over the years. Understanding why this happens can help us stay healthy as we age.
The hunger hormones and how they work
At its core, food intake has a functional purpose: without the energy we get from it, we simply would not survive.
Carbohydrates in our food are converted into energy, while fats and amino acids help form the vital proteins and other structures that support body functions.
To ensure that these processes run smoothly, the body has special systems that ensure a regular supply of energy.
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“These are self-regulating mechanisms that control hunger and satiety,” said Klaus. “They are mainly signals from the stomach and intestines, but also from hormones such as leptin, which is secreted by adipose tissue (or body fat) and sends signals to the hypothalamus (a control center in the brain). This is an autonomous system, like breathing.”
These chemical triggers that make us seek food (or stop seeking it) are sometimes called hunger hormones. Along with leptin, ghrelin is perhaps the best known hunger hormone.
Ghrelin is released from the stomach into the bloodstream and signals the brain that we should eat. When you are full, ghrelin release slows down, causing a feeling of satiety.
Other hormones also regulate the feeling of fullness and emptyness. These include insulin and other pancreatic hormones that suppress hunger, such as GLP-1, which mimics the diabetes drug Ozempic.
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The mechanics of digestion
When these hormones cause you to put food in your mouth, your body uses digestive processes to literally eat away at your meal.
Mechanical digestion begins in your mouth, where you grind your food into smaller, pulpier pieces that you can swallow. This process continues as the swallowed mush is pushed down your esophagus into your stomach – a process called peristalsis.
In parallel, chemical digestion takes place. This begins in the mouth, where amylase enzymes in saliva begin to break down the starch in food. More of these digestive enzymes are in the stomach to finish the job so that water and nutrients can then be absorbed from the intestines into the bloodstream.
How your appetite changes as you age
This urge to eat becomes stronger during puberty. The body needs energy to cope with its most important growth phase – puberty – and thus reach physical and sexual maturity.
But maintaining a healthy diet throughout life can be challenging. Older people are at risk of their bodies no longer being as effective at promoting the necessary nutrient intake. Some studies have shown that the secretion of hunger hormones changes in later life.
“As people get older, they lose muscle mass on average and muscles are the area that consumes the most energy,” said Klaus.
One of the main reasons for muscle mass loss is insufficient protein intake.
“Protein intake in later life is lower than recommended and even the recommendations according to various scientific groups for protein intake in later life should actually be higher because it is very important for maintaining muscle mass,” said Daniel Crabtree, a later-life nutrition researcher at the University of Aberdeen.
Despite this recommendation, Crabtree says protein intake among older people tends to be below the recommended amount, which may be related to physiological factors and other signs of aging in the body – from dental problems to changes in taste or smell.
