What is a healthy diet?
A healthy diet contains a wide range of fresh fruit and vegetables, whole grains, pulses, nuts and seeds. It is rich in important fibre and disease-busting antioxidants that protect against a number of illnesses and diseases including certain cancers and cardiovascular disease (Genkinger et al., 2004; He et al., 2007; Rautiainen et al., 2012). It has been suggested that the high concentration of antioxidants in blood may be one of the reasons for the lower incidence of chronic diseases in people consuming a plant-based diet rich in fruit and vegetables (Waldman et al., 2005). A healthy diet provides plenty of fibre protecting against a range of diseases including colorectal cancer (Murphy et al., 2012). It is rich in vitamins and minerals, again protecting health. A healthy diet should contain a good source of plant-based essential polyunsaturated fatty acids including the omega-3 fatty acids known to protect heart health (Pan et al., 2012).
On the other hand, a healthy diet should be low in saturated fat, animal protein and cholesterol for which we have no dietary requirement. Too much saturated fat can increase the amount of cholesterol in the blood, which increases your risk of developing heart disease. Saturated fat is found in many foods, such as hard cheese, cakes, biscuits, sausages, cream, butter, lard and pies. The government recommends that we eat less of these types of food and choose foods that contain unsaturated rather than saturated fats (NHS Choices, 2012). This means eating more avocados, nuts and seeds and plant-based oils and spreads such as flax seed oil and soya spread.
Cow’s milk, cheese, butter, cream, ice-cream and milk chocolate all contain the unhealthy saturated kind of fat associated with an increased risk of heart disease. Some of these foods contain considerable amounts of saturated fat. For example, Cheddar cheese contains around 35 per cent fat, of which over 60 per cent is saturated. Similarly, butter contains over 80 per cent fat, of which over 60 per cent is saturated (FSA, 2002). This means that a 10 gram serving of butter contains over five grams of saturated fat! The Government provide guidelines to tell you if a food is high or low in total and saturated fat (see Table 1).
Table 1. Government guidelines on fat content
|More than 17.5g of fat per 100g||High|
|3g of fat or less per 100g||Low|
|More than 5g of saturated fat per 100g||High|
|1.5g of saturated fat or less per 100g||Low|
So the five grams of saturated fat contained in just 10 grams of butter makes this food remarkably unhealthy. Plant-based polyunsaturated fat spreads contain less total fat (around 60 per cent) of which less than 20 per cent is saturated. They tend to contain more of the valuable polyunsaturated fatty acids and so provide a much healthier option.
Saturated fats from animal foods such as whole milk, cream and butter increase the amount of cholesterol in the blood which in turn increases the risk of heart disease and diabetes. Research shows that a plant-based diet contains significantly less saturated fat. The extensive EPIC Oxford study comprising 33,883 meat-eaters, 10,110 fish-eaters, 18,840 vegetarians and 2,596 vegans showed that while the total fat intake was highest in the meat-eaters and lowest in vegans, the difference between the groups was relatively small. However, the percentage of energy from saturated fat was strikingly different across the four diet groups: saturated fat intake was highest in meat-eaters, almost identical in fish-eaters and vegetarians and significantly lowest among the vegans (Davey et al., 2003). So significant is the lower saturated fat content of a plant-based diet that it can be used to control weight without worrying about calorie counting. In one clinical trial, adoption of a low-fat vegan diet was shown to help weight loss despite the absence of prescribed limits on portion size or energy intake (Barnard et al., 2005). Other research confirming that vegetarians and vegans have a lower risk of overweight and obesity than meat-eaters shows that consuming more plant foods and less animal products may help individuals control their weight (Newby et al., 2005). Being overweight or obese increases the risk of many health problems including type 2 diabetes, heart disease, asthma, infertility, high blood pressure and many cancers.
Milk and other dairy products contain many biologically active molecules including hormones and growth factors. Cow’s milk has been shown to contain over 35 different hormones and 11 growth factors (Grosvenor et al., 1992). Some researchers are particularly concerned about the oestrogen content of cow’s milk (Ganmaa and Sato, 2005), suggesting that cow’s milk is one of the important routes of human exposure to oestrogens. The milk consumed now is very different to the milk consumed a century ago. Unlike their pasture-fed counterparts of old, modern dairy cows are usually pregnant and continue to lactate during the latter half of pregnancy, when the concentration of oestrogens in blood, and hence in the milk, increases. Although there is a paucity of research in this field, early evidence suggests the increase in exposure to cow’s oestrogen may be linked to an increased incidence of certain cancers. In one study, cancer incidence was correlated with food intake in 40 countries (Ganmaa and Sato, 2005). Results showed that both cow’s milk and cheese increased the risk of hormone-dependent cancers such as breast and ovarian cancer. Among the dietary risk factors identified, these researchers were most concerned with milk and dairy products because, as already stated, the milk drunk today tends to come from pregnant cows among whom oestrogen and progesterone levels are markedly elevated.
Another bioactive component of cow’s milk receiving an increasing amount of attention is the growth factor called insulin-like growth factor 1 (IGF-1). The amount of IGF-1 present is higher in milk produced by pregnant cows. The concern is that because IGF-1 in cows is identical to human IGF-1, this growth factor could cross the gut wall and trigger an abnormal response, for example increasing the risk of certain cancers. It may be that IGF-1 does not cross the gut wall but that other bioactive components in milk boost IGF-1 production in the liver (see IGF-1). Either way, over the last decade IGF-1 has been linked to an increased risk of childhood cancers, breast cancer, lung cancer, melanoma and cancers of the pancreas and prostate (LeRoith et al., 1995; Chan et al., 1998) and gastrointestinal cancers (Epstein, 1996).
Interestingly, one study observed a 10 per cent increase in blood serum levels of IGF-1 in subjects who increased their intake of non-fat milk (Heaney, 1999) while another study noted that vegan men had a nine per cent lower serum IGF-1 level than meat-eaters and vegetarians (Allen et al., 2000). Whether the consumption of cow’s milk and dairy products raises IGF-1 levels directly (by crossing the gut wall), or indirectly (by triggering an increased production of human IGF-1 in the body), evidence suggests that some component of milk causes an increase in blood serum levels of IGF-1. It has even been suggested that IGF-1 may be used as a predictor of certain cancers, in much the same way that cholesterol is a predictor of heart disease (Campbell and Campbell, 2005).
In summary, a diet containing saturated fat, cholesterol, animal protein, hormones and growth factors is not a healthy diet. Cow’s milk, butter, cheese, cream, ice-cream and other dairy products contain all these unhealthy components whereas substantial evidence shows that a plant-based diet rich in fruit and vegetables, whole grains and unsaturated fats (including omega-3 fatty acids) offers significant health benefits. By adopting a healthy diet, together with regular physical exercise, avoiding smoking and drinking (alcohol) only moderately, many of the so-called modern Western diseases can be prevented. As part of its global strategy on diet, physical activity and health, the World Health Organisation (WHO) claims that up to 80 per cent of cases of coronary heart disease, 90 per cent of type 2 diabetes cases and one-third of cancers can be avoided by changing to a healthier diet, increasing physical activity and stopping smoking (WHO, 2003).