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by Tom Sanders
Our understanding of fats – including which ones are actually good for us – is evolving. We know for example that red meat and meat products, cakes and biscuits, which are rich sources of saturated fatty acids, are associated with an increased number of cardiovascular deaths. Conversely, nuts, oily fish and milk products, which are high in saturated fats, are associated with lower risk.
There are four main types of fats in our foods: polyunsaturated, monounsaturated, saturated and transfats. Each has different chemical and physical properties. Vegetable spreads and cooking oils – mainly rapeseed, sunflower, soybean and olive – usually contain the first two but relatively small amounts of saturated fat. But palm oil, which has a higher melting point and is now used in many products, is highly saturated.
Dietary advice, then, has moved away from the simplistic mantra that we should just eat less saturated fat, salt and sugar, towards a more discerning pattern that emphasises fruit, vegetables and low-fat dairy food, includes wholegrains, poultry, fish and nuts, and contains less red meat, sweets and sugar-containing beverages. But where do fats fit in? Here are ten things you may not know.
1. Fat is an energy food
Most of the energy in our diet comes from carbohydrates. But fat supplies between a quarter and two-fifths of an adult’s energy intake and half for a newborn. In babies, a high fat intake promotes fat deposits which insulate against heat loss.
Adding fat to food can double its energy content. Removing fat, from products like meat and milk, can substantially reduce it. Fat provides 9kcal/g (kilocalories/gram) in energy compared with 3.75kcal/g, 4kcal/g and 7kcal/g for carbohydrates, protein and alcohol.
2. Less energy intake, bigger weight loss
Reducing energy intake rather than increasing physical activity is the most effective means of reducing body fat. This can be achieved by using lower fat versions of existing foods, trimming fat from meat and using oils sparingly. There is not much difference in fat content between grilled and fried meat. Restriction of energy intake also requires limiting the intake of carbohydrates and alcohol.
3. Where it is in the body matters
Excess accumulation of body fat is most harmful if it is in the abdominal cavity or liver and is causally linked to developing type 2 diabetes. The use of a waist measurement (more than 80cm for women 94cm for men) indicates central obesity and is useful for predicting risk of type 2 diabetes.Women have more subcutaneous fat stores than men, so men store this visceral fat around the mesenteric blood vessel in the abdomen. When energy stored in fat cells is released, the fat mobilisation process leads to fatty acids entering the bloodstream. Visceral fat is more rapidly mobilised than subcutaneous fat and can accumulate in the liver. Fat also accumulates in the liver if the intake of alcohol or sugar is high.