Superfood claims need grain of salt

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Turmeric is said to be the latest "blockbuster nutrient", helpful for "everything from heart disease to Alzheimer's, asthma to arthritis".

But is there scientific evidence behind this claim, or is it just another example of the tendency to get hyped up about certain food components, which may be doing more harm than good?

Turmeric is the yellow spice that gives curry its familiar colour. It has been used as a traditional medicine in much of Asia for thousands of years. As for "blockbuster nutrient", I'm going to assume this implies a nutrient or food component that's especially powerful at preventing or curing disease.

There's good evidence that curcumin - the primary active component of turmeric - has many potentially beneficial biological properties, including antioxidant, , anti-inflammatory, anti-proliferative and anti-microbial activities. It shows promise in the treatment of a wide range of diseases, including Alzheimer's, Parkinson's, cardiovascular disease and cancer. But the authors of this latest paper say much of the evidence for its efficacy comes from laboratory studies that usually didn't involve humans.

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Curcumin clearly shows promise as a drug-like agent to treat disease (that is, it's extracted from turmeric, concentrated and then taken either through the mouth or by injection). But this doesn't mean that turmeric - the food that contains curcumin - promotes health.

We still need to work out whether eating it is the right way to make it have a therapeutic effect, and look into the possibility that it may have some untoward side effects. For example, there's some evidence that it may promote cancer under some circumstances.

So the jury is still out on whether turmeric truly qualifies as a blockbuster nutrient. Continue to enjoy the occasional curry, but it may be premature to start consuming large quantities of turmeric (or curcumin) on a daily basis just yet.

The claim that turmeric has some special properties (so people should eat large quantities each day) aligns neatly with "nutritionism".

This term was coined by Australian sociologist Gyorgi Scrinis to describe an undue emphasis on individual nutrients rather than on the diet as a whole. Nutritionism is therefore a kind of "reductionism", that is, the simplification of a complex idea until it's distorted.

It is based on the false premise that we know enough about nutritional science to accurately predict how intake of nutrients will impact on human health and well-being. He also points out that excessive concern over the effects of specific foods or components can lead to potentially harmful diets.

He sees three eras of nutritionism over the past century or so: the quantifying era, the good-and-bad era and the functional era.

The quantifying era took off with the discovery of vitamins about 100 years ago. This quickly led to claims they were lacking in the diet, so had to be taken as supplements.

Many people take supplementary vitamins, despite a lack of evidence that they help anyone other than those with vitamin deficiencies to the point of being ill. In fact, evidence suggests taking supplements may lead to earlier death.

In the era of good-bad nutritionism is fear of excessive intake of particular nutrients - fat-phobia and carbophobia, and that sugar is killing us - a throwback to British physiologist and nutritionist John Yudkin's 1972 call on sugar: "pure, white and deadly".

The "functional food" era began about 20 years ago with the development of foods modified to provide specific benefits.

Foods fortified with either long-chain omega-3 fatty acids (fish oils), plant sterols or probiotics are common.

There are instances where fortification is appropriate, such as folate to prevent neural tube defects. But unless there's a demonstrated benefit, or a diagnosis, it's best to ignore the latest fad and follow this simple but elegant recommendation by Michael Pollan: "Eat food. Not too much. Mostly plants." Bon appetit!

The Washington Post

Chris Forbes-Ewan is a senior nutritionist at Defence Science and Technology Organisation. He receives funding from Australia's National Health and Medical Research Council.