Dietary fat – restrict or free for all?

Cavemen's diet the latest fad.

Cavemen’s diet the latest fad.

A debate is raging about the amount of fat in the diet that is optimal for health and well-being. It has long been the prevailing view that saturated fat intake in particular should be restricted. As a result a range of fat-reduced food products appeared on the supermarket shelves. I happily stopped spreading butter or margarine on my sandwiches, selected low-fat greek yoghurt and low-fat milk, and trimmed fat from my meat.  I felt good.

Then around came Atkins promoting his Atkins Nutritional Approach that instead reduces carbohydrate intake. The diet limits consumption of carbohydrates to switch the body’s metabolism from metabolising glucose as energy over to converting stored body fat to energy. This process is called ketosis. Now I learned as a vet that ketosis in cattle and sheep can be life threatening so I didn’t go for this diet. So what should we believe? It gets worse. The Paleo diet, the latest fad, not only promotes restricting carbohydrates, but actively suggests that you should increase your fat intake. Live like the caveman to fit your genetic profile that hasn’t changed in the last 10,000 years! Are they mad (sorry, sorry all my paleo followers, feel free to provide comments if you like)?

Back to square one

In my total confusion, and I have to admit that I am subscribing to a few paleo blog sites just to find out what they do, I was so happy to see the results of a new study that I will briefly explain to you. In short, the study found that lowering dietary fat intake may lead to greater body fat loss than lowering dietary carbohydrate. Isn’t that great as it appeals to my sense of logic. And the study didn’t involve rats or mice, but real human beings, admittedly on the obese side.

In a first, the study set out  to investigate whether the same degree of calorie reduction, either through restricting only fat or restricting only carbohydrate, leads to differing amounts of body fat loss in men and women with obesity. They used 10 men and 9 women with obesity with an average age of 24 years and an average body mass index of 36 kg per meter squared. The participants were admitted to the metabolic ward of the National Institutes of Health (NIH) Clinical Center in Bethesda, Maryland and resided there 24 hours per day. All food eaten was strictly controlled and the daily activities of the participants were monitored.

Restricting fat intake produced the best results (Photo: fantasyhealthball)

Restricting fat intake produced the best results (Photo: fantasyhealthball)

For 5 days, everyone was fed a eucaloric baseline diet (consisting of 50% carbohydrate, 35% fat, and 15% protein) that gave them the exact number of calories they needed to maintain their body weight. For the next 6 days, the participants were randomly assigned to one of two groups where they received a 30% reduced-energy diet by having either their fat or carbohydrate intake restricted.

This was repeated after a 2- to 4-week washout period, but changed so that those who had eaten 6 days of reduced-fat diet in the first phase now ate a reduced-carbohydrate diet, and those who had eaten the reduced carbohydrate diet now ate the reduced fat diet.

And the result?

The researchers measured the amount of fat eaten and the amount of fat burned, and the difference between them determined how much fat was lost from the body during each diet. Compared to the reduced carbohydrate diet, the reduced fat diet led to a roughly 67% greater body fat loss.

Even if the trial included very few participants, the cross-over design used should produce accurate results. And the conclusion:

Calorie for calorie, reducing dietary fat results in more body fat loss than reducing dietary carbohydrate when men and women with obesity have their food intake strictly controlled.

Now that is good news. And just to put the record straight I do know that depleting your glucose stores by running for 30 minutes produces a ketogenic metabolism burning fat for the rest of your run. But this is only for a short time, while sticking to a ketogenic diet for many days might be a bit more dangerous.

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