For many years, the finger was pointed at fat for increasing the risk of obesity, heart disease, cancer and other diseases. Eating too much of certain types of fat can be harmful, but some fats are essential for normal body function and good health.
Why do we need dietary fat?
Fat is needed in the diet as an energy source. Gram for gram, it provides more than twice as many calories as carbohydrates and proteins (fat provides 9 calories per gram while carbohydrates, including sugars and proteins provide 4 calories per gram).
Fat supplies essential fatty acids such as linoleic acid and linolenic acids in the diet, is needed for the regulation of cholesterol metabolism, prostaglandin production and for the supply and/or absorption of fat soluble vitamins ( vitamins A, D, E and carotenoids).
Fats and health - The facts
Many nutrition recommendations in the 1980s and onwards called for low fat diets. High fat diets were thought to contribute to obesity, heart disease and cancer. However, many scientist are now questioning simple messages about fat reduction especially given emerging research that the type of fat may be at least as important as the amount of fat.
One of the biggest changes in recent years is the report from the World Cancer Research Fund last year which in contrast to previous reports did not specifically include a recommendation on fat reduction.
Cancer: The World Cancer Research Fund (WCRF) and the American Institute for Cancer Research report on 'Food, Nutrition, Physical Activity and the Prevention of Cancer' (2007) reviewed all of the science on dietary fats and oils and cancer risk.
"The report concluded that "…there is only limited evidence suggesting that diets relatively high in fats and oils (in total or any type) are in themselves a cause of cancer. This judgment contrasts with those of earlier reports which concluded from evidence then available that diets high in fats might be a substantial cause of some cancers".
Overweight and obesity: Body weight is determined by a complex interaction between genetic, metabolic, behavioural, environmental and cultural influences. In terms of dietary intakes, an increase in body weight occurs when we taken in more calories than we expend. Fats, providing twice the calories of proteins or carbohydrates may lead to weight gain if the excess calories are not balanced by physical activity. However an excess intake of calories from any source can lead to weight gain.
Heart disease: Excess intake of saturated and trans fats can increase blood cholesterol, a risk factor in the development of coronary heart disease (CHD). Trans fats can also lower high density lipoprotein levels. Recommendations to reduce the risk of heart disease are to replace saturated fats with monounsaturated fats and polyunsaturated fats and to keep the intake of trans fatty acids as low as possible.
A healthy body weight is also important in preventing cardiovascular disease. In the past low fat diets were the standard recommendation to prevent heart disease. However new research suggests that higher fat diets with better palatability may provide better heart health benefits provided the right type of fat is eaten.
A study comparing low fat (12% total fat) weight loss diets to those with a level of 35% monounsaturated fat but with equivalent calories reported that the diet high in monounsaturated fats lowered LDL cholesterol and oxidative susceptibility thereby lowering the risk of coronary heart disease.
Mediterranean populations eating traditional diets with high intakes of monounsaturated fats also appear to enjoy cardio-protective effects.
Achieving a healthy balance
Eating too many fats of any kind can be harmful to health but excluding fat can cause a dietary imbalance. The body requires 25 kg of fat a day to enable it to absorb fat soluble and beta carotene. Fats are also vital for provision of essential fatty acids (omega 3 and omega 6 fatty acids) which the body cannot produce itself.
Here are some tips for making sure the diet is balanced.
- Replace trans (check food labels for TFA content) and saturated fats (animal fats such as butter, the fat on meat) with monounsaturated (olive, canola, avocadoes, nuts) and polyunsaturated (safflower, sunflower) fats.
- Try to eat oily fish (such as salmon, tuna, sardines and mackerel) at least twice a week. These fish are excellent sources of omega-3 fatty acids.
- Choose low fat dairy products and lean cuts of meat trimmed of fat. Remove the skin from poultry.
- Eat natural source of fat such as nuts, seeds, grains, avocadoes and fatty fish to obtain extra nutrients and phytochemicals.
How much should you take daily?
Children 30- 60 g
Teenagers ( Active) 40- 80 g
Women 30- 60 g
Men (Active) 40- 80 g
Heavy Activity/Athlete 80- 120 g
Trans Fatty Acids
Hydrogenation is a process which adds hydrogen molecules directly to unsaturated fatty acids such as those found in vegetable oil. Hydrogenated oils contribute unique properties to foods- they make margarine more spreadable and pastries such as roti parata flakier. Trans fatty acids also occur naturally in meat and dairy products.
The US National Academy of Science has concluded that trans fatty acids have a similar effect to saturated fats on blood cholesterol- they raise low density lipoprotein (LDL) cholesterol. TFA's may also lower high-density lipoprotein (HDL) cholesterol. Intake of trans fatty acids should therefore be kept as low as possible.
(Food Facts Asia)