Nutrition (25 page)
Until as recently as 2004, healthy-eating recommendations suggested eating at least 55 per cent of calories as carbohydrate, emphasizing the quantity rather than the quality of carbohydrate consumed. It is only since 2005 that recommendations have started to focus on the type of carbohydrate consumed, and suggested that use of glycaemic index/glycaemic load would be more beneficial for health than considering total carbohydrates alone. Much of this change resulted from the popularity of low-carbohydrate diets, such as Atkins, which attracted a negative academic response and prompted a flurry of nutritional studies. Contrary to the entrenched carbohydrate-based paradigm, these started to show that a diet that supplied less than the usually recommended 45 per cent to 65 per cent energy from carbohydrates was associated with improved glucose control and triglyceride levels, ‘good’ HDL-cholesterol levels and could help some people lose weight. These studies also helped to underpin the growing recognition that a diet providing excess carbohydrates may have contributed towards the rise in obesity, Type 2 diabetes and nonalcoholic fatty liver disease.
We are now moving towards dietary recommendations that are based on quality rather than quantity of macronutrients as wholegrain cereals, unsaturated (i.e. polyunsaturated or monounsaturated) fat and protein play a beneficial role in promoting weight loss, insulin sensitivity, glucose tolerance and improved heart-disease risk factors such as lower blood pressure, cholesterol levels, inflammation and incidence of Type 2 diabetes.
Wholegrains and glucose control
Due to the fibre content and lower glycaemic load, the ‘brown’ wholemeal versions of grain-based foods fill you up for longer and have less impact on blood glucose levels so that less insulin is secreted, less glucose is pushed into adipose (fat) cells and appetite is suppressed for longer. As a result, a diet based on wholegrain products is associated with fewer long-term health problems such as obesity and Type 2 diabetes. This is why they are now seen as the foundation stone of a healthy but varied diet.
In 2004, a study published by the American Diabetes Association looked at 36,787 men and women without diabetes and followed them for four years. Those with the highest intake of white bread were 37 per cent more likely to develop diabetes over this period than those with the lowest intake. The researchers concluded that lowering the glycaemic index of the diet could reduce the risk of Type 2 diabetes, even when a high carbohydrate intake was maintained, and that one way to achieve this would be to substitute white bread for breads with a lower GI value.
Wholegrains and cardiovascular disease
Researchers now know that a high-glycaemic diet promotes obesity, insulin resistance, increases the production of triglyceride fats and small, dense LDL-cholesterol particles in the liver and reduces production of HDL-cholesterol. These adverse changes are associated with hardening and furring-up of the arteries and increased risk of coronary heart disease and stroke.
A pivotal study published in the
American Journal of Clinical Nutrition
in 2000, for example, looked at dietary glycaemic load, carbohydrate intake and risk of coronary heart disease in 75,521 women aged 38 to 63 years who were followed for ten years. The glycaemic load of each person’s diet was directly associated with their risk of having a heart attack, after adjusting for age, smoking status, total energy intake and other coronary heart-disease risk factors. Those with the highest glycaemic diet were twice as likely to have a heart attack over the ten-year follow-up period than those following a low glycaemic diet. The link between carbohydrate intake and heart disease risk was most marked in women who were overweight. This study suggests that a high glycaemic load from simple carbohydrates is an independent risk factor for coronary heart disease.
American Journal of Clinical Nutrition
in 2000, for example, looked at dietary glycaemic load, carbohydrate intake and risk of coronary heart disease in 75,521 women aged 38 to 63 years who were followed for ten years. The glycaemic load of each person’s diet was directly associated with their risk of having a heart attack, after adjusting for age, smoking status, total energy intake and other coronary heart-disease risk factors. Those with the highest glycaemic diet were twice as likely to have a heart attack over the ten-year follow-up period than those following a low glycaemic diet. The link between carbohydrate intake and heart disease risk was most marked in women who were overweight. This study suggests that a high glycaemic load from simple carbohydrates is an independent risk factor for coronary heart disease.
These results have consistently been verified in later meta-analyses and systematic reviews and, while some only showed an association between dietary carbohydrates and heart disease in women, recent Dutch and Finnish studies have shown that a higher total carbohydrate intake, glycaemic index and glycaemic load is associated with a higher risk of heart disease in men compared with lower intakes.
Wholegrains and cognitive function
Brain cells can only use glucose as fuel, not fatty acids. By promoting stable blood glucose levels, wholegrains promote optimum brain function, memory recall and concentration. A cereal breakfast is especially helpful for fuelling the brain as it boosts glucose levels at a crucial time of the day, after the long overnight fast. There appears to be a complex link between what you eat for breakfast and your biorhythms – carbohydrates only have a beneficial, alerting effect on mood if eaten in the morning on waking, and not when you eat them later in the day.
Studies show that schoolchildren who eat a wholegrain cereal breakfast perform better than those who don’t, with greater creativity, increased word power and an improved ability to solve problems and learn new information as well as more physical endurance.
Children’s exam results can also depend on whether or not they eat breakfast on the day of the test. Among one group of ten-year-olds, those who ate a cereal breakfast made fewer mistakes and worked more quickly in maths tests requiring concentration than those not eating an adequate breakfast. They also showed significant improvements in creativity.
Researchers have also found that adults who regularly eat a cereal breakfast are less depressed, less emotionally distressed and have lower stress levels than those not eating a cereal breakfast. They also have improved memory power, can recall new information more rapidly and have improved concentration and general mental performance. Of course, it’s possible that stressed people in stressful jobs are more likely to skip breakfast, but other research supports the fact that you need to eat after your overnight fast to lower secretion of stress hormones and to provide fuel for your brain.
Eating wholegrain cereals for breakfast can also greatly improve performance and endurance for athletes. This is particularly important for prolonged exercise activities such as long-distance running, cycling, triathlon and some team sports.
LESS WELL-KNOWN WHOLEGRAIN FOODS
Hemp pasta is made from flour and oil derived from hemp seed, which is related to sunflower seeds. Hemp seed has similar protein content to soybeans, and hemp-seed oil is a rich source of omega-3 oils and vitamin E.
Red rice (from Camargue or Bhutan) has a distinctive, nutty flavour and a satisfying, chewy texture due to the thin red bran that remains after light milling. It has the same nutritional value as brown rice but cooks twice as quickly.
Wild rice is the seed of a water grass. It is fermented for up to two weeks to make it easier to hull and to improve its nutty flavour. It is often mixed in with brown or red rice for added texture and visual interest.
Quinoa is the seed of a plant related to spinach. It has a slightly smoky flavour and is an excellent source of protein (50 per cent higher than most grains), vitamin E and B-group vitamins plus minerals such as potassium, magnesium, zinc, copper, manganese and folate.
Teff is one of the most ancient grains in the world, and also one of the smallest. Its name even comes from an old word ‘teffa’ meaning ‘lost’ because if you drop it on the ground you won’t find it again. Teff originated in Ethiopia as a foraged wild grass and was eventually cultivated by the highland Ethiopians. Teff is available in brown and white versions, but both are wholegrain as the kernel is too small to mill easily. Teff supplies more fibre-rich bran and nutritious germ than any other grain, and has a high mineral content including seventeen times more calcium than is found in wholewheat or barley.
Fruit and vegetables: why five a day?
Just about everyone is aware of the recommendations to eat at least five servings of fruit and vegetables per day, but where does this number come from? Why five a day rather than three, four, eight, or even more?
Plant foods are important dietary sources of fibre, phytosterols, isoflavones, carotenoids such as lutein and lycopene, minerals such as selenium and vitamins such as C and E. Most have a low glycaemic index and have beneficial effects on glucose control and insulin sensitivity. This is partly because the soluble fibre they contain helps to slow the absorption of dietary carbohydrates, and partly because their sugars include a blend of glucose and other fruit sugars, such as fructose, that have a lower glycaemic index. Whereas glucose has a GI value of 100, fructose has a GI of just 23.
Researchers have found that people who eat the most fruit and vegetables have a lower risk of developing a number of chronic diseases than those who eat the least. They help to protect against cancer, coronary heart disease, stroke and possibly diabetes. They may also reduce the risk of cataracts, diverticular disease, osteoporosis and obesity.
It is estimated that up to 70 per cent of all cancers are linked to poor diet. A review of over 200 clinical studies found a consistent protective effect of fruit and vegetables against cancers of the stomach, oesophagus, lung, mouth and throat, uterus, pancreas and colon, so the more servings eaten the better. The greatest protection came from eating raw vegetables, onions, garlic, carrots, green vegetables, members of the cabbage family and tomatoes.
People with a high intake of fruit and vegetables have a blood pressure that is around 5 mmHg lower than that of people with the least intakes. In this case, apples, oranges, prunes, grapes, carrots, alfalfa, mushrooms, raw spinach, tofu and celery were the most effective at lowering blood pressure. As a result, they help to protect against stroke. An analysis of eight studies involving over 257,000 people found that eating three to five servings of fruit and vegetables per day reduced the risk of stroke by 11 per cent, compared with those eating fewer than three a day. However, those eating more than five a day had a 26 per cent lower risk. Overall, it seems that each additional portion of fruit you eat per day reduces your risk of stroke by 11 per cent, while each additional portion of vegetables reduces your risk by 3 per cent.
As previously discussed, studies involving over 278,000 people have shown that eating three to five servings of fruit and vegetables per day reduces the risk of coronary heart disease by 7 per cent compared to eating fewer than three servings a day, and that those who eat more than five servings per day enjoy a 17 per cent lower risk.
When researchers in the US looked at the fruit and vegetable consumption of 9,665 adults aged 25 to 75 over 20 years, they found that eating at least five servings of fruit and vegetables per day reduced the risk of women developing Type 2 diabetes by almost 30 per cent – even after taking into account other risk factors such as age, weight, cigarette smoking, blood pressure, cholesterol levels, physical inactivity and alcohol consumption. Vegetables that were the most beneficial for blood glucose control were green leafy vegetables (such as cabbage), beans and some tubers such as Jerusalem artichoke. However, a meta-analysis of data from five large studies involving over 167,000 people found that eating five or more servings of fruit and vegetables per day only reduced the risk of developing Type 2 diabetes by around 4 per cent. This was considerably lower than expected. When the same authors looked at nine studies assessing the antioxidant intake of almost 140,000 people, they found that antioxidant intake, rather than fruit and vegetables, reduced the risk of Type 2 diabetes by 13 per cent, and this was mainly attributed to vitamin E. Reasons for these discrepancies are unclear, and more research is needed.
Overall, however, the evidence suggests that eating five servings of fruit and vegetables per day is good, but that eating
more
than five is considerably better, and that nine to ten servings appears to be the ideal. Potatoes are not classed as a vegetable, but are included in the starchy class of foods.
more
than five is considerably better, and that nine to ten servings appears to be the ideal. Potatoes are not classed as a vegetable, but are included in the starchy class of foods.
Each of the following amounts is equivalent to one serving:
• one whole apple, orange, pear, peach, nectarine, kiwi, banana, pomegranate or similar-sized fruit
• two satsumas, plums, apricots, figs, tomatoes or similar-sized fruit
• half a grapefruit, guava, mango, Gaia melon, avocado
• a handful of grapes, cherries, blueberries, strawberries, dates
• a handful of chopped vegetables such as carrots, cabbage, sweetcorn, broccoli florets (and protein-rich pulses such as beans, peas, lentils, chickpeas)
• a small bowl of loosely packed, mixed salad stuff
• a small bowl of vegetable soup
• a wineglassful (100 ml) of fruit or vegetable juice (these only count towards a maximum of one serving per day, as they contain little fibre).
Juice your own
Fruit juices can only count as one serving per day, however much you drink, but although you remove much of the insoluble fibre from fruit or vegetables when juicing, you obtain considerably more micronutrients than when eating all your fruit and vegetables in their natural raw state. The secret is in their concentration. One hundred millmetres of carrot juice can give you as much betacarotene as one pound of raw carrots.
Smoothies can count as two servings if they contain at least two full servings of whole fruit rather than just the juice.
It is worth investing in a juicer to prepare your own delicious juices. Freshly prepared juice has a creamy texture, a milky hue and is richer in vitamins and antioxidants than those that have sat on a shelf or in a fridge for several days. Once you’ve tasted the home-made version, you’ll never be fully satisfied with those sold in bottles, cartons or cans again.
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