Coconut oil is a highly saturated fat, and one of the few of these fats that doesn't come from animals. Like other saturated fats, coconut oil has been viewed in the past as unhealthy because it is capable of raising cholesterol levels. For that reason, I have recommended that it should play only a very limited role, if any, in your diet. Evolving scientific thinking about the role of saturated fats in heart disease may lead to new recommendations about them, but we're not there yet.
As you note, in recent years, some extravagant claims have been made for coconut oil, none of which is supported by solid scientific evidence. We don't know how it affects cholesterol levels – so far, I've seen in only one study that it raises both HDL ("good") cholesterol and LDL ("bad") cholesterol. Whether it alters the risk of heart disease is unknown. We do know that Polynesian peoples who consume the oil from fresh coconuts as their main dietary fat do not have high rates of heart disease.
Beyond that, lauric acid, the main saturated fat in coconut oil, has been credited with antibacterial, antimicrobial, and antiviral properties. It has been used to treat colds and flu, cold sores and genital herpes, genital warts, gonorrhea, yeast infections, chlamydia and other infections. However, we do not have good evidence for its efficacy in most of these conditions.
The claims that coconut oil can help you lose weight stem from the fact that it is mostly composed of medium-chain triglycerides (MCTs), which go from the intestinal tract directly to the liver where, it is believed, they are burned as fuel rather than being stored in body fat. The one study that carefully examined the effects of coconut oil on weight loss was a small one, with only 40 women participating. Half of them used two tablespoons of coconut oil for cooking daily while the others used soybean oil. All the participants cut 200 calories from their daily diets and exercised four days a week. After three months, the women in both groups had each lost about two pounds. In other studies, dieters who used MCT-rich oil extracted from coconut lost more weight than those who used vegetable oil, but the losses reported were modest. To date, I've seen no study that has shown using coconut oil leads to significant weight loss.
Many investigations have used partially hydrogenated coconut oil, which is made from coconut meat that has been dried, pulverized and chemically treated. A healthier product, called "virgin" or "cold-pressed" oil, is extracted more gently from fresh coconut meat, but it still has a lot of saturated fat.
I've read recent claims that coconut oil benefits Alzheimer's disease patients. It is true that MCT-rich oil from coconuts has been studied in Alzheimer's patients, but this treatment has not led to improvements of the patients' scores on cognitive tests. All told, I think the jury is still out on coconut oil, and without stronger evidence for it, I hesitate to recommend eating it in quantity.
Andrew Weil, M.D.