By Peta Bee, published in The Times on 4th September 2018
Diet by the decades: what to eat and when to eat it
Boost your vitamin D
Peak growth spurts tend to be about the age of 12½ for girls and 14 for boys. Teenagers need more protein than adults (boys need about 55g daily, girls about 45g) to feed their muscle mass increases. Eggs, fish, beans and lentils are the best sources.
At this age a large amount of bone mass is laid down, so calcium and vitamin D are needed. Boys aged 11 to 18 need 1000mg of calcium a day and girls 800mg, which can come from a combination of a glass of milk, 45g of cheese and a yoghurt, or more green leafy vegetables, nuts and sardines.
A study in 2016 found that even in summer, most 14 to 18-year-olds in Britain did not have an adequate supply of vitamin D. Dietitian Helen Bond says: “It’s often down to what I call gaming deficiency and is common among those who are on electronic devices a lot.”
About 10mcg a day is required from age 11 upwards and you can get it from food (orange juice, tinned tuna, milk and fortified cereals are good sources).
Teenagers also need extra iron for healthy blood; girls will need more (14.8mg a day) than boys (11.3mg a day) after they start menstruating. Low levels are linked with poor appetite, increased risk of infection and lower activity and focus. The best source is red meat, followed by soya beans, lentils, chickpeas, cooked spinach, prunes and raisins. Fatigue is a sign that they may not be getting enough. If that is confirmed by a blood test, a supplement might be prescribed.
At exam time, eating dark chocolate might give teenagers a boost. Its high levels of polyphenols and a small dose of caffeine improved brain function in a study conducted by David Kennedy, the director of the brain, performance and nutrition research centre at Northumbria University.
Psychologists and nutrition scientists found a significant boost in the performance of teenagers who had consumed a juice or smoothie made of 220g of fresh blueberries two hours before an exam. A mixed berry drink (75g each of strawberries, raspberries, blackberries and blueberries) boosted brain-derived necrotrophic factor and improved cognitive performance six hours later.
Beware of going dairy-free
Studies have shown that most people who adopt healthy habits in their 20s stay healthy well into middle age. But it is also when bad habits kick in.
Bone building continues through this decade, so it is important to eat plenty of calcium, perhaps trying more adventurous ingredients such as firm tofu and tahini.
The fashion for dairy-free eating has meant that an iodine deficiency is increasingly common in this age group.
It is needed for the production of thyroid hormones, and too little can lead to thyroid disorders, resulting in low energy levels and poor metabolism.
Other than cow’s milk, it’s in white fish, eggs and seaweed.
Eating for fertility
In this decade, men and women need to make sure they eat enough magnesium, a mineral that helps to generate energy, regulate blood pressure and blood sugar, and maintain strong bones. It can also help reduce feelings of stress and irritability: “Stress can cause the immune system to take a battering at this age and folic acid, zinc and magnesium are vital for combating the effects,” says Bond.
Men need 300mg and women 270mg of magnesium daily, from pumpkin seeds, almonds, cooked Swiss chard or spinach, cashews, plain yoghurt and wheat bran. A 10-year study in the US found that men in their 30s who ate 75g of pistachios daily were better equipped to cope with the rigours of daily life. The nuts appeared to help arteries to relax in response to stressful situations, lowering blood pressure.
A recent review showed a strong correlation between eating oily fish and a lower frequency of infertility
A recent Harvard review showed a strong correlation between eating walnuts, soya beans, chicken, turkey, wholegrains, fruit and vegetables and oily fish and a lower frequency of infertility. This range of nutrients boosted fertility in women and semen quality in men, the researchers said.
They found that evidence to support the idea that alcohol and caffeine can hamper fertility was “less solid” than previously thought. A study in the journal Andrology last month suggests a moderate alcohol intake (four to seven units a week) is linked with higher semen volume, sperm concentration and total sperm count. Another recent study shows men in their early 30s who ate two handfuls of mixed almonds, hazelnuts and walnuts daily for 14 weeks improved their sperm count and motility.
In May, a study of 5598 first-time mothers found that those who avoided highly processed meals conceived almost a month earlier than women who ate them four or more times a week before they became pregnant. Jessica Grieger of the University of Adelaide says the high amounts of saturated fat, sugar and salt are to blame. Studies in mice demonstrated a high-fat diet had a toxic effect on their ovaries, she says.
Eat less food, eat more plants
The WHO estimates that our basal metabolic rate, the amount of energy needed to maintain ordinary body functions, decreases by an average 2.9 per cent in men and 2 per cent in women every decade from now on.
Recommendations are for women to consume up to 2000 healthy calories until the age of 51 and men to eat about 2500. However, some experts think we need fewer: “Recent studies of people aged 35 to 50 have found their metabolic requirements are over-estimated and it’s unlikely they need the amount suggested,” says Sarah Schenker, a dietitian and co-author of The Ageless Body.
“They probably need more in the region of 1600 (women) and 2100 (men); more if you do a lot of exercise.”
Include foods high in vitamins C and E and selenium, antioxidants that lower the risk of inflammatory disease and cancer. There’s plenty of vitamin C in berries, red and green peppers, citrus fruit, kiwis, brussels sprouts and tomato juice, and vitamin E in sunflower seeds, almonds, sunflower oil, hazelnuts and peanut butter, and selenium in brazil nuts, tuna and turkey.
“Getting beta carotene from carrots, sweet potato and apricots will also help to build up the body’s defences against serious diseases,” Bond says.
Oestrogen starts to dip in women, testosterone in men: “A plant-rich diet is important for both as it provides hormone-stabilising nutrients,” says Bond. Foods rich in vitamin K, such as eggs, brussels sprouts, broccoli, prunes and kefir, along with those rich in zinc — oysters, mussels, shellfish, beef, pumpkin seeds, spinach and cashews — are natural testosterone boosters for men.
Now is the time to plan your dietary attack against prostate cancer. Cutting down on alcohol helps. So does eating more foods rich in lycopene, an antioxidant that can protect against DNA and cell damage.
Tomatoes are one of the best sources: a study shows men who consumed more than 10 portions a week in a variety of forms — including tomato juice and baked beans — saw their risk of prostate cancer drop by 18 per cent.
Switch to porridge for breakfast
For women, changes in the menstrual cycle can lead to higher losses of iron. “Include plenty of vitamin C-rich kiwi fruit, peppers and tomatoes, as well as meat, eggs and wholegrain iron sources, as vitamin C helps to increase iron absorption from other foods,” Schenker says.
Studies show that female hormone levels can be balanced by eating foods rich in plant oestrogens, such as soya, linseeds, chickpeas and lentils. About 80 per cent of women in the West reportedly experience perimenopausal symptoms (lethargy, mood swings, interrupted sleep) compared with only 14 per cent in Asia, where there is a higher daily intake of these beneficial plant compounds, called isoflavones.
An intake of 700mg a day (same as for men) of calcium is needed to help to counter the rapid bone loss that occurs when bone-protective oestrogen levels plummet because of the menopause. If you don’t eat dairy products — the best source — include other calcium-rich foods such as green leafy vegetables, almonds, sesame seeds, dried fruit, pulses, fortified soya drinks and tofu. Kennedy has found that nitrates in beetroot, rhubarb and leafy green vegetables improve cerebral blood flow and performance in mental tasks.
Age will take a toll on skin health, so men and women should ramp up their intake of vitamin C, beta carotene and vitamin E, which boost collagen.
And if you don’t already, start eating porridge for breakfast. “It contains soluble fibre that binds bile acids in the gut so that they cannot be reabsorbed into the body,” Schenker says. “Since more cholesterol is needed to make new bile acids, it leaves less swimming around in the blood, which is good news for your heart.”
Boost your fibre intake and eat more oily fish
Pak choi, chard, okra and asparagus will boost your intake of folate, for healthy blood, and potassium, which is key to regulating blood pressure. They are also an essential source of fibre, now believed to have anti-ageing benefits.
Chronic gut inflammation caused by a diet low in fibre is believed to make our bodies store more excess calories as fat as we get older. “Add linseeds or chia seeds to your breakfast cereal, swap white bread for wholemeal, eat grains such as pearl barley, quinoa and wholegrain rice,” says nutrition therapist Ian Marber.
There’s evidence too that the long-chain omega 3 fatty acids in fish oils can help to reduce the harmful inflammatory processes that accelerate ageing. Symptoms such as cracked nails, dry skin, fatigue and depression potentially stem from a lack of essential fatty acids. If you don’t like mackerel, sardines or tuna, get some omega 3 from seeds (pumpkin, chia and hemp) or nuts (pecan, walnut and hazelnut), as well as nut oils.
Foods fermented with bacteria, but not vinegar, can help to keep digestive issues at bay. Marber suggests unpasteurised cheeses, kombucha tea, yoghurt and sauerkraut.
Adding sage and herbs to your cooking could benefit cognitive function. “We have consistently seen improvements in brain function with sage and other herbs,” says Kennedy. Bond says: “People neglect eye nutrition and yet age-related macular degeneration is the biggest cause of blindness from 60 onwards. You need a good intake of eye nutrients such as lutein and zeaxanthin, found in egg yolks, peppers, kale and spinach.” A study last month shows eating an orange a day cuts the risk of failing eyesight in the elderly by as much as 60 per cent.
Beware of B12 deficiency and dehydration
With age, men and women have a reduced capacity to synthesise vitamin D from sunlight. “Eat plenty of oily fish, eggs and mushrooms to get enough,” Schenker says.
Some older people are prone to vitamin B12 deficiency. Fatigue and a sore, red tongue, as well as balance problems, are symptoms. It causes a form of anaemia, so make sure you get enough from yeast extract or red meat.
You can help avoid digestive problems by consuming plenty of prebiotics — foods that feed gut bacteria. Eat leeks, onions, wheat, chicory root, garlic and artichokes, and banana and asparagus, as well as foods with insoluble fibre, such as wholegrains and avocados, says Glenn Gibson, head of food microbial sciences at the University of Reading. A study from the US shows older adults who eat the most leafy vegetables — one or two servings a day — score better in tests of mental ability than those who eat less.
Our thirst receptors become less effective as we age and dehydration is common. “Too little fluid — you need approximately two litres from drinks, soups and water-based salad foods and fruit — can result in confusion and a sharp drop in attention span,” says Bond.