|
|
|
Health without milkIs milk really good for you? An increasing amount of research challenges the out-dated notion that cow’s milk is the best source of calcium and in fact shows that our consumption of dairy products is doing us much more harm than good. The Vegetarian and Vegan Foundation answers some frequently asked questions... How much calcium is in these foods? Milk is a natural food… isn’t it? Don’t children need milk for calcium? Doesn’t most of our calcium come from milk? What is the link between cow’s milk and diabetes? How easily is calcium absorbed? Which other nutrients help calcium absorption? What if we don’t eat enough calcium? Doesn’t cow’s milk protect against osteoporosis? What increases our risk of osteoporosis? How does animal protein promote calcium loss? What other factors are important for bone health? Can a vegan diet supply sufficient calcium?
Calcium is a soft grey metallic element. It is the fifth most abundant element on the earth’s crust and occurs in compounds such as limestone, chalk and marble. This important mineral plays a central role in maintaining bone health and strength; around 99 per cent of our calcium is deposited in the bones and teeth, the other one per cent is involved in the regulation of muscle contraction, heart beat, blood clotting and functioning of the nervous system. The UK government currently suggest that the reference nutrient intake (RNI) value for calcium in adults aged between 19 and 50 years of age is 700 milligrams per day. While milk and dairy products do contain calcium, plant-based sources provide a much healthier source. Good plant-based sources include green leafy vegetables such as broccoli, kale, spring greens, cabbage, parsley and watercress. Also rich in calcium are dried fruits such as figs and apricots, nuts, particularly almonds and brazil nuts and seeds including sesame seeds and tahini (sesame seed paste). Pulses including peas, beans, lentils and calcium-set tofu (soya bean curd) provide a good source of calcium as does molasses. How much calcium is in these foods? The following table shows how much calcium is present in a range of calcium-rich foods.
Milk is a natural food… isn’t it? All mammals drink the milk of their mothers until they are weaned. Unlike all other mammals though, humans continue to drink milk after weaning and into adulthood, and not just that, we drink the milk of another species! To state the obvious (but often overlooked fact) cow’s milk has evolved to help turn a small calf into a cow in less than a year. That’s why cow’s milk contains around four times as much calcium as human milk. Calves need a huge amount of calcium to promote the massive level of skeletal growth required over the first year of life. A human infant does not require such high levels of calcium; indeed the high mineral content of cow’s milk puts a strain on the human infant kidney which is why most governments strongly recommend that children do not drink normal ‘off the shelf’ milk in the first year. Don’t children need milk for calcium? No, what they do need is exercise and ahealthy plant-based diet. A recent review on dairy products and bone health (Lanou et al., Pediatrics 2005) shows that there is very little evidence to support increasing the consumption of dairy products in children and young adults in order to promote bone health. This review examined the effects of dairy products and calcium on bone strength in children and young adults and found that physical exercise is the most critical factor for maintaining healthy bones, followed by improving the diet and lifestyle; this means eating plenty of fresh fruit and vegetables, and for young adults cutting down on caffeine and avoiding alcohol and smoking. Doesn’t most of our calcium come from milk? No, less than half (43 per cent) of the calcium in the average UK diet comes from milk and milk products. This was reported in 2004 in the Food Standards Agency’s National Diet and Nutrition Survey. So despite the misconceived notion that milk is the best (or only) source of calcium the facts show that a large share of the calcium in our diets is derived from sources other than dairy foods. This is not surprising as most people in the world (around 70 per cent) obtain their calcium from plant-based sources rather than dairy products. Lactose intolerance is the inability to digest lactose, the sugar in milk. In order for the sugar in lactose to be digested it must be broken down in the gut by the enzyme lactase into its two component sugars (glucose and galactose). Most infants produce lactase for a while but lose the ability to digest lactose after weaning (commonly after the age of two). Losing this ability is a clear indication that after weaning, milk is not a natural food for us. Lactose intolerance occurs in around 90-100 per cent of Asians, 65-70 per cent of Africans, and 10 per cent of Caucasians. Symptoms include nausea, cramps, bloating, wind, and diarrhoea. If you suffer from lactose intolerance you should avoid all dairy products. Milk allergies occur when the body’s immune system perceives one of the proteins (casein or whey) in milk as a foreign invader and launches an attack. Symptoms are usually more extreme than in lactose intolerance and include excessive mucus production resulting in a runny nose and blocked ears. More serious symptoms include eczema, colic, diarrhoea, asthma and vomiting. The milk protein casein is difficult to avoid as it is commonly used in the production of bread, processed cereals, instant soups, margarine, salad dressings, sweets and cake mix. What is the link between cow’s milk and diabetes? Early exposure to cow’s milk formula has been linked to an immune response that can lead to type I diabetes in some children. The immune response involves the body’s immune system reacting to a trigger (which may be cow insulin or a protein called casein from cow’s milk). Structural similarities between the triggering molecule and the insulin-producing pancreatic beta cells confuse the human immune system and it attacks the cells in the pancreas. This limits the ability to produce insulin and may lead to diabetes. The avoidance of cow’s milk during the first few months of life may reduce the risk of type I diabetes in some children. How easily is calcium absorbed? The calcium in dairy products is not absorbed into the body as easily as that in many dark green leafy vegetables. For example, calcium is much more easily absorbed from kale than cow’s milk. However, while spinach contains a lot of calcium, it is bound to a substance called oxalate which inhibits calcium absorption, so it is important to obtain calcium from low-oxalate green vegetables (eg broccoli, cabbage, bok choy, watercress). Grains, nuts and seeds contain a substance called phytic acid which until recently was also considered to hinder calcium absorption; however phytic acid is now believed to have only a minor influence. Caffeine and smoking has been shown to reduce calcium absorption. Which other nutrients help calcium absorption? Several other nutrients help calcium absorption. Vitamin D is very important for calcium absorption, it is either obtained from the diet or it is made in the skin following exposure to sunlight. Vitamin D deficiency may occur if exposure to the sun is limited and without sufficient vitamin D, calcium deficiency is likely to occur even if the diet provides enough calcium. The consequences may be serious, resulting in rickets or osteomalacia (softening of the bones). Over the last few years there have been cases of vitamin D deficiency in some large UK cities. Vegans obtain vitamin D from sunlight and fortified foods such as soya milks, cereals and margarines. It is important to get the balance right between being cautious about exposure to the sun and aware of the need for some exposure. It is now advised by the UK government that we apply sun block after 10 to 15 minutes exposure to the sun, this is so that we can synthesis vitamin D in the skin.Furthermore, magnesium, potassium, vitamin C, and vitamin K, are all required for good bone health. A healthy diet that includes at least five servings a day of fruit and vegetables should optimise the intake of these and other micronutrients required. What if we don’t eat enough calcium? When the diet does not provide enough, calcium is reabsorbed from the bones to restore blood levels and maintain calcium-dependent functions. If enough calcium is then supplied in the diet, bone levels are restored, but if the diet fails to supply sufficient calcium, bone loss persists. Doesn’t cow’s milk protect against osteoporosis? No, osteoporosis occurs most commonly in countries where they drink the most milk! American women are among the biggest consumers of calcium in the world yet they suffer one of the highest levels of osteoporosis, while African Bantu women eat almost no dairy products at all and have a relatively low calcium intake from vegetable sources yet osteoporosis is virtually unknown among Bantu women. Increasing milk consumption does not protect against bone fracture, in it may be that an increased calcium intake from dairy foods increases the risk of fracture. What increases our risk of osteoporosis? Calcium loss from the bones is promoted by high intakes of animal protein. By the age of 80, vegetarians tend to have lost less bone mineral compared to omnivores. Research suggests that the more animal protein you eat, the higher your risk of hip fracture becomes. Cross-cultural studies show strong links between a high animal protein diet, bone degeneration and the occurrence of hip fractures. In a rural community in China where most of the protein in the diet came from plant foods rather than animal foods, the fracture rate was one-fifth of that in the US. How does animal protein promote calcium loss? As food is digested, acids are released into the blood and the body attempts to neutralise the acid by drawing calcium from the bones. This calcium is then excreted in the urine (the calciuric response). Animal protein has a particularly bad effect because of the greater amount of sulphur-containing amino acids it contains compared to plant protein. As the sulphur content of the diet increases so does the level of calcium in the urine. If the diet cannot keep up with the loss of calcium from the bones then ultimately the bones will become weaker. The traditional Inuit (or Eskimo) diet is made up almost entirely of animal protein. Inuits potentially have one of the highest calcium intakes in the world; up to 2,500 mg a day depending on whether they eat whole fish, including the bones, or not. They also have a high rate of osteoporosis, even higher than white Americans! What other factors are important for bone health? Physical activity is a key factor in reducing osteoporosis risk. To promote bone health and reduce the risk of osteoporosis it is important to get enough vitamin D, reduce caffeine and alcohol intake and not smoke. Many studies suggest exercise is the most important factor. The best type of activity for bone health is weight bearing exercise; this includes walking, stair climbing and dancing. Can a vegan diet supply sufficient calcium? Yes it certainly can. There are no scientific reports of calcium deficiency in adult vegans. Looking solely at calcium intake and not at calcium losses tells only half the story, while a vegan’s intake might be less than a meat eater’s, their losses are likely to be much lower. The evidence is that a plant-based diet free of animal products - a vegan diet - doesn’t produce these losses. A vegan diet rich in vegetables, fruits and whole grains can provide the basis for a long and healthy life, reducing the risk of osteoporosis and many other diseases. In contrast, diets loaded with dairy products are associated with increased risk of osteoporosis, certain cancers, heart disease, obesity and diabetes.
|
