However, on examining the evidence, it appears that a reasonable amount of saturated fats in the daily diet may be essential for health and longevity - preventing heart disease, osteoporosis and even cancer.
Saturated fats are mostly from animal foods, but are also found in tropical oils like palm and coconut oils. The saturated fats in our diets are generally derived from four types: stearic (animal fat and chocolate); lauric (coconut oil); palmitic (palm oil, animal products and dairy); and myristic (coconut oil and dairy).
Humans have ingested saturated fats since the dawn of time, and saturated fatty acids are found in breast milk, and are essential for infants and toddlers. They provide taste, consistency and stability to foods.
Saturated fats cushion and provide energy to the kidneys and, without palmitic fats, important signalling and stabilising processes in the body will falter. When these fats are lacking, cell and organ growth factors become dysfunctional. People with a deficiency of saturated fats in their white blood cells (T cells) eventually show a decline in immune function.
Myristic acid stabilises proteins, including those used by the immune system and those that fight tumours. The effects of stearic fatty acids on cholesterol are neutral, or may help by lowering cholesterol. Lauric acid is antimicrobial (see box, page 19).
Greasing the wheels
Over 60 years ago, Cleveland dentist Weston A. Price became intrigued as to why it was that children living in isolated regions exhibited physical near-perfection, while the American children in his dental practice suffered from all manner of ailments. He found that, although the traditional diets varied, they all had one thing in common: whole, natural foods devoid of white flour, refined sugar and rancid vegetable oil.
Further analysis showed that native diets included more than 10 times the amounts of fat-soluble vitamins A and D - found only in animal fats, organ meats, fish, eggs and shellfish - than did the typical British or American diet. These vitamins are essential for healthy bones, for preventing birth defects and reproductive problems, for proper growth and development, and for preventing diseases such as colon cancer and multiple sclerosis.
We need saturated fats to absorb these and other nutrients, such as vitamin K, associated with blood-clotting and building bones. Vitamin K is also more available from dairy products than from green beans or green leafy vegetables, and is better absorbed from vegetables eaten with butter than eaten plain (Br J Nutr, 1996; 76: 223-9).
Scientists such as Linus Pauling, John Yudkin and Mary Enig have long known that, while the consumption of saturated fats has declined, heart disease has continued to soar. So, how can saturated fats be to blame? Why do people in, say, Puerto Rico, who consume a diet high in animal fats, have such a low incidence of breast and colon cancers - diseases supposedly linked to saturated fats (Cancer Res, 1975; 35: 3265-71)? Also, the fact that Spain has just one-third the breast-cancer death rate of France or Italy - despite having the highest total dietary fat intake of the three - shouldn't make any sense either, unless you accept the idea that saturated fats may not be at fault.
Indeed, Dr Enig found that, contrary to popular belief, analysis of the United States Department of Agriculture (USDA) data shows that the supposedly 'good fats' - polyunsaturated fats from vegetable oils (corn, soy, safflower and the like) - appear to predispose people to cancer, whereas animal fats may be protective. When she published her concerns back in 1978, she was among the first to point the finger at trans fats, made by 'hydrogenation', where hydrogen is added to a liquid vegetable oil to turn it into a solid. It is only now - 25 years later - that steps are finally being taken to eliminate these nasty fats, which are present in most processed foods, from our food supply.
The real culprits
Trans fatty acids (t-FAs) have been shown to raise low-density lipoprotein (LDL, or 'bad') cholesterol in the blood, according to reviews of all the data. Unlike saturated fats, trans fats lower high-density lipoprotein (HDL, or 'good') cholesterol, leading to greater risks of heart disease and stroke (J Am Coll Nutr, 1996; 15: 325-39).
Polyunsaturates also have evidence of damage. This makes sense as polyunsaturates go rancid easily on exposure to air, heat and light. Such oxidation forms cell-damaging free radicals.
A study of more than 60,000 Swedish women, aged 46-70, found that polyunsaturated fats are associated with an increased incidence of breast cancer, while saturated fats were not (Arch Intern Med, 1998; 158: 41-5).
As for heart disease, when male albino rats were fed a diet high in polyunsaturated fats such as soybean and rapeseed oils, they showed a high incidence of heart lesions. But, when dietary saturated fats (from cocoa butter) were added to the oils, the number of lesions was significantly reduced (Lipids, 1982; 17: 372-82).
So, saturated fats may have heart-healthy aspects after all (although findings in animals may not apply to humans).
However, a three-year study of postmenopausal women with heart disease found that, contrary to the negative dogma, those who regularly consumed more saturated fats actually had less disease progression than those who followed a diet higher in polyunsaturated fats and carbohydrates (Am J ClinNutr, 2004; 80: 1175-84).
Protection against disease
A follow-up of the Swedish Malmo Diet and Cancer Study, which studied the fat intakes of 28,000 middle-aged people for five years, observed no ill effects of a high saturated-fats intake in either men or women (J Intern Med, 2005; 258: 153-65).
Some scientists believe saturated fat may even be cardioprotective. Although coconut oil is a predominant constituent of the traditional diets of the Pukapuka and Tokelau Polynesians in the South Pacific, vascular disease is not common in either population (Am J Clin Nutr, 1981; 34: 1552-61).
Lipoprotein a, or Lp(a), found in the bloodstream, is a marker for cardiovascular disease. In one double-blind study comparing the effects of eating different types of fats - oleic acid (monounsaturated fats such as in olive oil), and different concentrations of trans fats and saturated fats - the diet that included saturated fats lowered Lp(a) by 8-11 per cent (Arterioscler Thromb Vasc Biol, 1997; 17: 1657-61).
In India, scientists attribute the increase in heart disease and type 2 diabetes to the replacement of traditional cooking fats, such as ghee (clarified butter) and coconut oil, with polyunsaturated vegetable oils (J Indian Med Assoc, 1998; 96: 304-7).
Finally, saturated fats in our mucous membranes can inactivate viruses, bacteria, fungi and protozoa (Ann NY Acad Sci, 1994; 724: 457-64).
Dr Enig has arrived at the heretical conclusion that adults should consume a whopping 25 per cent of their entire calories as saturated fats. (The USDA's Dietary Guidelines for Americans 2005 recommend only 10 per cent.)
The evidence thus far is clear: for a healthy heart and bones, it may be wiser for us to resolve to stop blaming fats, and to look instead to processed foods, which may well be behind the epidemic of 'unhealth' in our modern societies today.