A healthy diet

Foods and nutrients

When you look at a plate of lentils you see seeds cooked in a broth, but after digesting it your body extracts iron for the red blood cells, protein for the muscles and starch to obtain energy. How does what you put in your mouth differ from the chemical substances that your cells actually use?

The Food Pyramid

No food is banned. What matters is how often and how much. A plate of lentils with vegetables sits on the lower shelves and can be eaten every day. Chicken nuggets and chips are top-shelf foods, for now and then.

The Mediterranean diet as a model

The traditional Mediterranean diet, from countries around the Mediterranean Sea, is often used as a model of healthy eating, and it is useful to compare with how we eat in Ireland. Every day it includes vegetables, fruit, pulses, wholegrain cereals and nuts. Olive oil is the main fat. Fish and seafood are eaten a few times a week, eggs and poultry in moderation (a few times a week), and red meat and sweets only occasionally (a few times a month). Many teenagers' diets today look very different: more crisps, sweets, fizzy drinks and takeaways, and fewer vegetables, fruit and pulses. The Irish Food Pyramid points the same way: most of your food from the bottom shelves.

Organising meals according to needs

A healthy diet combines variety, water as the usual drink and foods of good nutritional quality. Spreading meals out helps to organise the day, but there is no energy figure or compulsory distribution that is valid for every teenager: growth, activity and personal circumstances all play a part.

A common pattern is five eating occasions: breakfast, a snack at mid-morning break, lunch, an afternoon snack and dinner. Spreading food over the day gives your body and brain a steady supply of energy, helps you concentrate in class and stops you getting so hungry that you overeat later.

Breakfast matters because you have not eaten for ten hours or more. A good breakfast mixes carbohydrates for energy (porridge, wholemeal bread), protein (milk, egg) and some fruit for vitamins and fibre.

Ultra-processed foods and sugars

It is advisable to prioritise varied foods, with plenty of plant-based foods, and to limit products with too much salt, free sugars or poor-quality fats. 'Processed' does not always mean unhealthy: tinned cooked pulses can form part of a balanced diet.

Ultra-processed foods are industrial products made mostly from ingredients you would not use in your kitchen at home, such as flavourings, colours, sweeteners and emulsifiers. You can spot them in the shop by a long ingredients list full of unfamiliar names and by ready-to-eat packaging: crisps, sweets, fizzy drinks, chicken nuggets, instant noodles. We should limit them because they are usually high in sugar, salt or fat, low in fibre, easy to overeat and heavily advertised. They are tasty and cheap, but they often replace fruit, vegetables and pulses in the diet.

A fizzy drink gives empty calories: energy from free sugars but almost no vitamins, minerals or fibre. A whole orange gives similar sugars plus water, fibre, vitamin C and potassium. Because fibre slows digestion, blood glucose rises gradually after the orange. After the fizzy drink it shoots up quickly and then drops, leaving you tired and hungry again. Squeezing the fruit into juice removes most of the fibre, so juice behaves more like a sugary drink than a whole fruit.

Water, fibre and essential nutrients

Your body is about 60 per cent water. Every day you lose water in urine, sweat and your breath, so water is the nutrient you need to replace most often. You can live for weeks without food, but only a few days without water.

If you lose more water than you take in, you become dehydrated: thirst, headache, tiredness, poor concentration and dark urine. Severe dehydration is dangerous. Drink water regularly, especially in hot weather or at GAA training.

Nutrients are also split into two kinds. An essential nutrient cannot be made by your body (or not in enough amount), so it must come from food: for example vitamin C, iron, calcium, some amino acids (the building blocks of proteins) and omega-3 fats. A non-essential nutrient can be made by your body from other substances: for example cholesterol, and some amino acids such as alanine.

Judging a menu

To judge a menu, follow these steps. Sort each food onto the Food Pyramid. See which shelves are missing or overused. Check fibre, fruit and vegetables, and what is being drunk. Then suggest swaps. Never just ban foods: think about how often you eat them.

Another quick check is the plate model (a simple way to apply the Irish Food Pyramid and the Healthy Eating Guidelines): fill about half your plate with vegetables and fruit, a quarter with wholegrain foods (wholemeal bread, brown rice, wholewheat pasta) and a quarter with protein foods (fish, chicken, eggs, beans). Use healthy oils in small amounts and drink water.

Be careful with adverts. 'Contains vitamins' can be true of a single lettuce leaf. Ask three questions: how much of each food is there, how processed is it, and what is missing?

Eating for growth and sport

In your teens you grow fast, so you need plenty of energy, protein, calcium for bones and iron for your blood. If you play hurling or rugby you need more energy and more water than someone who does not, but you do not need a special diet.

Your brain runs on glucose from carbohydrates. A breakfast of only a glass of milk gives protein and calcium but little carbohydrate, so by mid-morning your blood glucose can fall and you feel tired and cannot concentrate. Adding porridge or wholemeal toast and a banana fixes this.

Food labels give energy in both kJ and kcal, per 100 g and often per portion, so you can work out how much energy you are really eating. The nutrition table also gives total sugars and salt per 100 g; the ingredients list tells you which sugars have been added.

Most teenage athletes get enough protein from a varied diet: milk, yoghurt, eggs, meat, fish, beans and nuts. Extra protein does not build more muscle. Training and enough energy do that, and the excess is used for energy or stored as fat. Protein shakes and other supplements are expensive, may be poorly regulated and can contain substances that are not on the label. Ask your GP or a dietitian before taking any.

A plant-based diet can be healthy if it is planned. Combine beans, lentils, tofu, nuts and wholegrains for protein. Eat iron-rich foods such as lentils, dark green vegetables and fortified cereals, with a source of vitamin C to help absorb the iron. Vitamin B12 is found almost only in animal foods, so vegans need fortified foods or a supplement. Fortified plant milks give calcium. A diet of jam on toast, plain pasta and salad has very little protein or iron.

Salt and comparing labels

Use the 'per 100 g' column to compare two products of the same kind, because portion sizes differ. Look at sugars, saturated fat, salt, fibre and protein. Then read the ingredients list. Ingredients come in order from the largest amount to the smallest, so if sugar is near the top, the product contains a lot.

Salt (sodium chloride) gives no calories, but sodium affects how water moves in your body. When you take in a lot of salt, your body holds on to extra water to dilute it. More fluid in the blood vessels raises blood pressure, and over the years this strains the heart and blood vessels. The WHO limit of 5 g of salt a day is for adults, and it is somewhat less for children. Much of our salt is hidden in crisps, ham, rashers, sausages, soups and bread.

Eating well is more than knowing

Knowing what is healthy is not always enough: a pupil can pass a test on the Food Pyramid and still eat poorly, because choices depend on what is available and affordable. Rates of childhood overweight can rise even when most pupils know the guidelines, so the cause is not simply a lack of information. Our food environment matters too: prices, how many fast-food outlets are near school, advertising, time, income and culture. That is why public health measures, such as healthy school meals, calorie labelling on menus and the tax on sugary drinks, work alongside information.

Eating disorders are illnesses, not a lack of willpower or a lifestyle choice. Anorexia nervosa involves severely restricting food, an intense fear of gaining weight and big weight loss. Bulimia nervosa involves bingeing followed by trying to get rid of the food, and weight can stay in the normal range. Warning signs include skipping meals with excuses, constant worry about calories, avoiding eating with others and distress around food. They can harm growth, bones, the heart and mental health. Early help makes recovery more likely. You cannot diagnose a friend, but you can be kind, avoid comments about weight and tell a trusted adult. Your GP, the school guidance counsellor and Bodywhys, the Eating Disorders Association of Ireland, can help.

Back to the beginning: Aoife's lunchbox gives her carbohydrates from the brown bread for steady energy, fibre and vitamins from the apple, and, if the sandwich has chicken or egg, protein for growing muscles. The crisps are a top-shelf extra: fine now and then, not every day.

Summary