Saturday, November 02, 2013

The dietonomics of fat. Correlation does not mean causation

Repeat after me.

In economics as in medicine one of the easiest mistakes is to assume that correlation means causation.

In 2010 two of the biggest names in international economics produced a study showing that when a nation’s government debt hit 90 per cent of gross domestic product its economic growth fell. Politicians used the finding to promote austerity in Europe, with unfortunate results. But the researchers hadn’t proved causation. It was just as likely that low economic growth caused the high debt to GDP ratio as it was the other way around.

Science writer Gary Taubes who was interviewed on the Catalyst program believes that’s how it is with fat.

People who are fat either eat more than thin people or do less exercise. We’ve come to believe it’s the eating or lack of exercise that’s making them fat. But it could be the other way around. Their body’s compulsion to store and hold fat might be forcing them to eat more and stripping them of the energy they need to exercise.

Sugar creates such a compulsion. It produces insulin which pushes fatty acids into fat cells and temporarily locks them there removing a source of energy. Its why people feel weak as they are eating a sugary or carbohydrate-laced meal and hungry for more.

Taubes says that in contrast fat itself doesn’t do that. Taken without carbohydrate fat doesn’t make us fat. After all, we have been eating it for millennia and sugary foods are relatively recent. Which would mean the traditional food pyramid should be turned on its head. Instead of being told to eat only small amounts of fat and large amounts of carbohydrate we should be told to do the reverse (except that we couldn’t eat large amounts of fat - it satisfies rather than builds an appetite). But changing the advice would mean organisations such as the Heart Foundation admitting they have been wrong. Cardiologist Ernest Curtis ruefully told Catalyst, “that’s not going to happen”.

And it would antagonise incredibly important industries. How would the sugar industry cope if food producers tried to remove it from virtually every processed product? How would the grains industry react if we were advised to abandon porridge, corn flakes and bread in the morning?

Part of a larger piece for the Sydney Morning Herald on the ABC Catalyst controversy

Below, Robert Lustig explains the damage caused by sugary foods.

Warning: The video is 90 minutes! (Watch the rest later here)

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. Why are we eating more?

. Coca cola, busted