Guiding principles to lose weight are fairly basic. Here Dr CLIVE HUNT, senior lecturer in nutrition at Huddersfield University’s School of Applied Sciences, explains matters
AS spring and summer approach (hopefully!), thoughts may turn to losing those few extra pounds ready for the beach holiday!
In one sense the answer is obvious; eat fewer calories (and exercise more). But this is easier said than done. Countless diets have come and gone over the years and different approaches will suit different people.
However, there are some important facts and guiding principles which have emerged from scientific research and which are worth bearing in mind in relation to diet and weight control.
Playing a central role in all of this is the fat in your food.
Firstly, fat, whatever the type, is the most concentrated source of energy in the diet having nine kcals/g compared with alcohol at seven, and protein and carbohydrate at four.
Water, of course, has no calories and therefore the energy content of any food is largely dependent on the fat and water content, so that a high-fat, low-water food has to be high-calorie and a low-fat, high- water food will be low-calorie.
We can alter calorie content of food in processing and a good example is the humble potato. Baked and boiled potatoes are relatively low calorie, being virtually fat-free and having a relatively high water content.
However, removing the water and adding fat, as in crisps (which are over 30% fat by weight), turns it into a high-calorie food (in fact more calories per 100g than double cream!).
Obviously how many calories we get from a food will depend on both its calorie density (calories per 100g) and the weight of food eaten, but there may be more subtle factors at play as well.
Many people eat a relatively high fat diet with approximately 40% of calories from fat, but we are recommended to reduce to about 30%. This is partly to reduce cardiovascular risk in the long-term but it is also relevant to weight control.
Evidence from historical research, plus studies on primitive tribes, suggest that we evolved over hundreds of thousands of years on a low fat diet, probably no more than 20-30% calories from fat, so our high fat diet is a relatively recent phenomenon.
We now know that our sensations of hunger and appetite are controlled by a sub-conscious and primitive part of the brain know as the hypothalamus.
Here is located the satiety centre which receives many chemical and electrical messages from around the body informing us of our calorie intake and stores and hence whether we need to eat or not.
Generally the satiety centre does a good job in regulating our energy balance (calorie intake versus calorie expenditure) but, critically, what recent research has shown is that the centre is much more likely to make small but significant positive errors on a high fat diet (which it didn’t evolve to cope with, as mentioned) than a lower fat diet.
Over time this can lead to substantial weight gain and even obesity, particularly if combined with a sedentary lifestyle.
So what’s the answer? Well, evidence is increasingly showing that lowering the calorie density of the diet can help a great deal.
This effectively means avoiding too much fatty food (and alcohol!) and ‘diluting’ calorie density with low fat, higher water, foods such as fruit and vegetables and also cereal (bread, pasta, rice, etc) and potato products that have not had a lot of fat added.
But does this work in practice? Various studies, including a recent one of obese women in America, suggest that it does. They were advised to eat ad lib but to cut down on fatty foods.
This led to substantial and sustained weight loss, even more so when they were also advised to increase fruit and vegetable consumption.
We need some fat from our food, but avoiding too much appears to be critical to weight control.