Sunday, May 9, 2010

The skinny on fat and heart risk

May 8, 2010

By Andy Ho

A RECENT story in the Scientific American magazine highlights a just-published study that found 'no association between the amount of saturated fat consumed and the risk of heart disease'.

Data from several studies had been pooled together to compare what people reported about their daily food intake with their likelihood of developing coronary heart disease (CHD).

However, nutritional studies based on self-reporting are always difficult to do well. This is because people, especially if they have weight problems, tend to be biased in their recall of what they eat. Pooling such errors together could magnify results even further.

After all, rigorous epidemiological studies have repeatedly shown that a high intake of saturated fats (and a special type of it called trans fats) is associated with heightened CHD risks. Saturated fats in red meat, dairy products and tropical oils are the main dietary causes of raised cholesterol levels.

A 2007 Lancet study pooling data on almost 900,000 subjects from 61 studies confirmed that as blood cholesterol levels rise, the incidence of CHD rises exponentially, and so too does the mortality rate from heart ailments.

The Scientific American report thus goes against well-attested facts. Next, it tries to show that not only are 'saturated fats... not so bad (but) carbohydrates could be worse'. The claim is that the real culprit in CHD is carbohydrates - starchy foods such as bread, rice, potatoes, pasta, noodles and so on.

That is the gospel of Dr Atkins' New Diet Revolution (2001). The bestseller led to a fad diet that Hollywood celebrities still rave about. The Atkins diet blames carbs for the world's obesity epidemic, and hence CHD.

Carbs, it argues, cause the body to overproduce insulin, a hormone that provokes hunger pangs, which leads to more eating. As insulin induces body cells to store excess carbs as fat, the kilos mount. So cut the carbs, insulin levels stay low, and less fat is stored.

In actual fact, proteins and fats both stimulate insulin production. Any excess of carbs or proteins or fats is stored as fat. That excess fat, whatever its origins, cranks out bioactive molecules (such as interleukin-6 and leptin). These molecules promote damage to the internal lining of arteries, which fosters atherosclerosis. This is why the obese face higher CHD risks.

This means an excess of proteins or fats is as bad as an excess of carbs, and vice versa. The Atkins scheme is wrong when it advises a diet of unlimited portions of protein and fat - pork chops, beef steaks, lard, butter - so long as virtually no carbs are consumed.

The Scientific American story quotes a 2008 study showing that Atkins dieters 'lost twice as much weight' as those on conventional low-fat diets. Indeed, several other studies have confirmed that Atkins does lead to more weight loss than the standard low-fat diet - at least initially. But this is not because of the carbs restriction per se.

Since protein satisfies one's appetite, there is little craving for carbs. Because the carbs reduction is so drastic, one's overall caloric intake falls compared to one's baseline. It is this reduced calorie intake that sustains later weight loss after the initial period in an Atkins scheme.

The body stores some carbs as glycogen in the liver and muscles. In the initial period of Atkins, with no carbs available, glycogen is burnt off to supply one's energy needs. But every gram of glycogen is bound to three grams of water. Thus, when glycogen is broken down, a lot of water gets excreted as well.

Continuing with the diet, a body deprived of carbs soon resorts to oxidising its own store of fat to help meet energy needs. This leads to the production of ketones, molecules with the ability to increase urine production.

Thus by causing water losses through both routes, a low-carb diet rapidly leads to a dramatic weight loss. This early weight loss and the diet's unusual character make Atkins an effective weight-loss diet.

However, it has now been consistently shown in many studies that Atkins does not outperform other diets in the long run. Several rigorous studies have found greater weight loss through Atkins than conventional diets in the first six months, but no significant weight difference over 12 months.

Studies do show that Atkins lowers one's triglycerides, fats also involved in CHD, and that it raises (good) HDL cholesterol. Critically, however, Atkins raises (bad) LDL cholesterol.

In fact, bad cholesterol typically decreases with weight loss in all diets - except low-carb ones. This is probably because of the extremely high intake of saturated fats through unlimited meat consumption permitted in Atkins.

It is now established that, when it is starved of carbs, the body overproduces methylglyoxal, a chemical that causes blood vessel and tissue damage. Heart rhythm problems have also been noted.

So is Atkins safe over the long run? Recently, two huge European studies that had followed dieters over a decade were published. In both studies, people who had been on low-carb, high-protein diets for years faced significantly higher risks of dying from CHD.

More deaths from cancer were also noted in one of the two studies. Taking too little grain, fruit and vegetables for years may have led to a higher incidence of cancer.

In sum, extended periods of carb deprivation could shorten lives. A low-carb diet and the consumption of excess saturated fats might be equally bad for one's health.

[All diets other than a balanced diet with regular and adequate exercise are just fads. You can't cheat nature and you can't cheat death. ]

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