THE FACTS ON FATS

Conventional thinking over the last few years (decades for that matter) has been that fat makes you fat and that if you quit eating fat, you'll lose weight without even trying. Afraid to say, but it doesn't work - as you've probably already learned.

DOES EATING FAT REALLY MAKE US FAT?

Because fat is, well, fat, it has a reputation for being fattening. . The idea here is that the fat we eat requires little chemical transformation before it is stored as fat under our skin and elsewhere in our bodies. 

Saturated fat is also blamed for the rising obesity rates seen in many countries because it contains roughly twice as many calories as carbohydrate or protein. So, in theory, eating a lot of fat means consuming a lot of calories, something which one might expect to increase our risk of piling on the pounds. 

IS A CALORIE A CALORIE?

The concept that fat’s calorific nature is inherently fattening is founded in the principle that eating more calories than we burn metabolically in the body will lead to weight gain. This ‘calorie principle’ forms the basis of pretty much all advice ever given to individuals wishing to lose weight. This usually translates into a blanket recommendation to those wanting to shed pounds to eat less and/or exercise more. When weighing up calorie balance in the body, most health professionals do not distinguish between different types of calories. In other words, the general view appears to be a calorie is a calorie is a calorie, and that the form it comes in is quite irrelevant.  

This obsession with calorie balance seems to have blinded most health professionals to the fact that different types of calories are ‘burned’ differently in the body, and some burn more efficiently than others. We can think of the body’s metabolism as rather like a fire which, say, easily burns small bits of dry wood, but has more difficulty with larger, soggy pieces of wood. Could it be that for some individuals, eating fat is like putting small, dry pieces of wood on that fire?  

One way to put this theory to the test is to assess the weight loss effects of diets that contain the same number of calories, but are made up of varying amounts of fat, carbohydrate and protein. If it’s only the total number of calories that count, then diets that contain the same number of calories should have the same effect on weight, irrespective on the composition of the diets. Actually, studies show this simply isn’t the case.  

In one study, for instance, the effects of two diets of different composition were assessed in a group of women over a 6-month period. Each of these diets contained exactly the same number or calories, but one had 35 per cent of calories coming from fat, where the other had just 21 per cent. Women in both groups lost weight, but, tellingly, the women eating more fat lost significantly more (7.7 kg versus 4.7 kg).  

In another study in women, the effects of a diet based almost entirely on carbohydrate was compared with one in which half the calories came from carbohydrate, with the other half coming from almonds (a fatty food). Again, both these diets contained the same number of calories. Over 24 weeks, the almond-eating group actually lost 50 per cent more weight (an additional 16 lbs) over 24 weeks than their carb-consuming counterparts.  

In yet another study, this time in men. researchers compared three diets that contained the same amount of calories, but varied in the relative amounts of fat and carbohydrate they contained. Individuals eating the most fat (and least carbohydrate) lost the most weight, while those eating the least fat (and most carbohydrate) lost the least.  

What these studies show is: 

• It’s not just the number of calories we consume, but the form they come in, that has an influences body weight 

• Eating a diet relatively rich in fat is not, in itself, a barrier to weight loss 

• Actually, all things being equal, eating more fat and less carbohydrate tends to lead to more effective weight loss  

HOW EFFECTIVE ARE LOW FAT DIETS FOR WEIGHT LOSS?

The only way to know if dietary fat is a potent force in obesity is to test this with appropriately designed studies. One way to do this is to put individuals on a low-fat diet to see what effect this has on body weight.  

In order to get an idea of the overall effect of low fat eating on weight, several relevant studies were assessed in a review published by the highly-respected international group of researchers known as the Cochrane Collaboration in 2002. The researchers were particularly interested in the ability of participants to sustain weight loss over a long period of time.  

The average amount of weight lost in low-fat and control diets were assessed at 6, 12 and 18 months. The following table summarises the findings of this review. 

Average weight change on low fat diet (Kg)

Average weight change on control diet (Kg)

6 months

- 5.08

-6.50

12 months

- 2.30

-3.40

18 months

+ 0.1

-2.30

 

You will see from this table that any initial weight loss seen on a low-fat diets declines in time. This was also true of the control diets, but not nearly to the same extent. 

In fact, the control diets out-performed the low-fat diets at every stage. And perhaps most importantly of all, at 18 months, those instructed to eat low-fat diets had, on average, actually gained weight, while those eating control diets had lost some. This is not the only review of the evidence to find that low-fat diets are less effective than control diets where weight loss is concerned.