Alex Johnstone, University of Aberdeen

Do you eat to live or live to eat? We have a complicated relationship with food, influenced by cost, availability, even peer pressure. But something we all share is appetite – our desire to eat. Increased appetite might have a physical or psychological dimension, but while hunger – our body’s way of making us desire food when it needs feeding – is a part of appetite, it is not the only factor. After all, we often eat when we’re not hungry, or may skip a meal despite pangs of hunger. Recent research has highlighted that the abundance of food cues – smells, sounds, advertising – in our environment is one of the main causes of overconsumption.

Our appetite is not fixed, it changes across our lifespan as we age. But as our choice of food will be an important factor to our health and well-being throughout our lives, it’s important that we get into the right habits. As Shakespeare might have put it, there are seven ages of appetite, and a better understanding of these phases would help us to develop new ways of tackling under-eating and overconsumption, and particularly the health effects such as obesity that follow.

First decade, 0-10

In early childhood the body goes through rapid growth. Dietary behaviour built up in early life can extend to adulthood, leading a fat child to become a fat adult. Fussiness or fear of food can contribute to meal time struggles for parents of young children, but a strategy of repeated tasting and learning in a positive environment can help children learn about unfamiliar but important foods, such as vegetables.

Children should experience some control, particularly in relation to portion size. Being forced to “clear the plate” by parents can lead youngsters to lose their ability to follow their own appetite and hunger cues, promoting overeating in later years. There are growing calls for governments to protect young children from targeted junk food advertising – not just on television but in apps, social media and video blogs – since food advertising increases food consumption, contributing to becoming overweight.

Second decade, 10-20

In the teenage years, a growth in appetite and stature driven by hormones signals the arrival of puberty and the development from child into adult. How a teenager approaches food during this critical period will shape their lifestyle choices in later years. This means the dietary decisions adolescents make are intrinsically linked to the health of the future generations that they will be parents to. Unfortunately, without guidance teenagers may adopt eating behaviours and food preferences associated with unhealthy consequences.

We need more studies to determine the most effective ways of tackling the rising burden of over and under-nutrition, particularly the link with poverty and social inequality. Young women in general are more likely to suffer from nutritional deficiencies than young men because of their reproductive biology. Teenage girls who become pregnant are also at greater risk since their body is supporting their own growth in competition with that of the growing foetus.

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Third decade, 20-30

As young adults, lifestyle changes that can prompt weight gain include going to college, getting married or living with a partner, and parenthood. Once accumulated, body fat is often difficult to lose: the body sends strong appetite signals to eat when we consume less than our energy needs, but the signals to prevent overeating are weaker, which can lead to a circle of over-consumption. There are many physiological and psychological factors that make eating less difficult to maintain over time.

An area of new research interest is to develop satiety, the sense of having eaten enough. This is helpful when trying to lose weight, since feeling hungry is one of the main limitations to managing to eat less than your body is telling you you need – running a “calorie deficit”. Different foods send different signals to the brain. It’s easy to eat a tub of ice cream, for example, because fat doesn’t trigger signals in the brain for us to stop eating. On the other hand, foods high in protein, water or fibre content are able to make us feel fuller for longer. Working with the food industry provides an opportunity to shape the future of meals and snacks in beneficial ways.

Fourth decade, 30-40

Adult working life brings other challenges: not just a rumbling stomach, but also the effects of stress, which has been shown to prompt changes in appetite and eating habits in 80% of the population, equally divided between those that gorge and those that lose their appetite. The different coping strategies are intriguing: the phenomena of “food addiction” – an irresistible urge to consume specific, often high-calorie foods – is not well understood. Many researchers even question its existence. Other personality traits such as perfectionism and conscientiousness may also play a role in mediating stress and eating behaviour.

Structuring the work environment to reduce problematic eating patterns such as snacking or vending machines is a challenge. Employers should strive to subsidise and promote healthier eating for a productive and healthy workforce – particularly ways of managing stress and stressful situations.

Fifth decade, 40-50

We are creatures of habit, often unwilling to change our preferences even when we know it is good for us. The word diet comes from the Greek word diaita meaning “way of life, mode of living”, yet we want to eat what we want without changing our lifestyle, and still have a healthy body and mind.

There is much evidence to show that diet is a major contributing factor to ill-health. The World Health Organisation highlights smoking, unhealthy diet, physical inactivity and problem drinking as the main lifestyle impacts on health and mortality. It is in these years that adults should change their behaviour as their health dictates, but symptoms of illness are often invisible – for example high blood pressure or cholesterol – and so many fail to act.

Sixth decade, 50-60

The gradual loss of muscle mass, at between 0.5–1% per year after the age of 50, begins and continues a steady course into old age. This is called sarcopenia, and lessened physical activity, consuming less than protein requirements, and menopause in women will accelerate the decline in muscle mass. A healthy, varied diet and physical activity are important to reduce the effects of ageing, and an ageing population’s need for palatable, cost-effective, higher-protein foods is not being met. Protein‐rich snack foods might represent an ideal opportunity to increase total protein intake in older adults, but there are currently few products designed to meet the requirements and preferences of older adults.

Seventh decade, 60-70, and beyond

A major challenge today in the face of increasing life expectancy is to maintain quality of life, or else we will become a society of very old and infirm or disabled people. Adequate nutrition is important, as old age brings poor appetite and lack of hunger, which leads to unintentional weight loss and greater frailty. Reduced appetite can also result from illness, for example the effects of Alzheimer’s disease.

Food is a social experience, and changing factors such as poverty, loss of a partner or family and eating alone affect the sense of pleasure taken from eating. Other affects of old age, such as swallowing problems, dental issues, reduced taste and smell (“sans teeth … sans taste”) also interferes with the desire to eat and the rewards from doing so.

We should remember that throughout life our food is not just fuel, but a social and cultural experience to be enjoyed. We are all experts in food – we do it every day. So we should strive to treat every opportunity to eat as an opportunity to enjoy our food and to enjoy the positive effects eating the right foods have on our health.

Alex Johnstone, Personal Chair in Nutrition, The Rowett Institute, University of Aberdeen

This article was originally published on The Conversation. Read the original article.