Messages from health authorities, food manufacturers, diet books and internet gurus can be contradictory ...
Knowing what to eat is not always simple. Nutrition land is often full of flip-flopping advice; carbs are bad, then good - and then they are bad all over again.
The messages from health authorities, food manufacturers, diet books and internet gurus can be contradictory but a new book, Coffee Is Good for You, makes it easier to tell the believable from the bodgie.
Its author, the American health writer Robert J. Davis, unpicks the evidence to give his verdict on nutrition claims. Here are some of the common assumptions he tackles ...
COFFEE IS BAD FOR YOU
False. Coffee's unhealthy reputation stems partly from old research that links it to an increased risk of heart disease and pancreatic cancer but fails to account for the effects of any cigarettes that might have been smoked with the coffee. Newer studies have found coffee drinkers have no greater risk of heart disease or stroke. In fact, they may have a slightly lower risk. Overall, research shows no extra risk for cancer, either - and a lower risk for Parkinson's disease. Though caffeine has been linked to a higher risk of miscarriage, up to 200 milligrams of caffeine daily (one or two cups) is generally considered safe for pregnant women. Nevertheless, moderation makes sense; more than three cups daily is linked to bone fractures in women who get too little calcium.
CINNAMON IS EFFECTIVE AGAINST DIABETES
Inconclusive. After discovering that a substance in cinnamon acted like insulin - at least in a test tube - US researchers gave people with type 2 diabetes a daily dose of cinnamon, and dummy pills to a control group. After 40 days, the cinnamon group had lower levels of blood glucose and cholesterol, while there was no change in the control group. Other research results have been inconsistent - possibly because not all of those studied have had diabetes and because researchers have not always accounted for other dietary factors that can affect blood glucose levels.
SOY WARDS OFF CANCER
Inconclusive. The theory is that substances in soy called isoflavones inhibit the development of breast and prostate cancers. With prostate cancer, this is backed by animal studies but human studies are mixed. Some animal studies have shown soy promotes breast cancer but a study of 5000 Chinese breast cancer survivors suggests eating more soy decreases the chances of cancer recurrence and death. Other human studies show no effect. Davis speculates the amount and type of soy might matter. Pro-soy results generally come from studies in Asia, where soy consumption is high and food such as miso and tofu are generally made from whole soybeans. In the West, much of our soy comes from soybean extracts in processed food, which may be less beneficial or even harmful.
CHOCOLATE IS GOOD FOR YOU
Half true. Many short-term experiments - often funded by the food industry - show that chocolate, especially the dark stuff, improves the health of blood vessels, lowers blood pressure and does not raise "bad" LDL cholesterol. Long-term studies of elderly men, middle-aged people and heart-attack survivors link greater chocolate and cocoa intake to less heart disease and stroke. But some studies used almost 100 grams of chocolate daily and this could lead to weight gain. Davis's advice? Eat dark chocolate, make sure the main ingredient is cocoa or chocolate liquor, not sugar - and don't expect miracles.
Coffee Is Good for You by Robert J. Davis (Perigee, $19.95) is out now.
Paula Goodyer blogs at smh.com.au/chewonthis
