Friday, August 14, 2009

Why some people find it hard to lose weight - there could be a scientific reason

This article hopefully removes some of the burden of trying to loose weight. Here is some scientific facts as to why for some people it is such a uphill battle.

Firstly we have to take responsible for our weight and secondly to loose weight you need eat less energy than you give out. It is simple but not easy! We all know people who struggle to lose weight. They put lots of effort into exercise and focus on healthy eating but they seem to unable to easily slim down.

Due to personal experience of seeing this occur I have always wondered why some find weight management easy and some find it very difficult. I have always suspected that there is more going on at a cellular level than we understand. Well this week in browsing my personal journal collection I uncovered an amazing paper. The bottom line is that some people who are obese have less ability to turn fat into energy. Thus it is harder to burn off the fat. Their body at a biochemistry level does not help, and even restricts their ability to lose weight.

For those interested I will unpack the science:

Non Esterified Fatty Acids (NEFA) "float" around in your blood, making up about 10% of fat in the blood. They are also known as Free Fatty Acids (FFA) which seems a simpler name so I will used FFA for the rest of the article. In fasting these fats increase in the blood as FFA is pumped into the blood from fat stores, so that cells can absorb them and then use the for energy.

Muscles of obese men and obese women who have fat on their stomachs (viscerally-obese) when injected with a substance (beta- adrenergic) that should promote cells uptaking FFA does not promote any FFA uptake. This is despite the blood FFA's being the same level as non obese people whose muscles do take up FFA after injection. This implies that their bodies restrict fat burning at a cell level.

Even more disturbing is that weight reduction does not seem to reverse this lack of fat uptake. That is if an obese person has impaired FFA uptake, loosing weight does not cause the muscle cells to return to "normal" and absorb fats properly. This could be of the reasons that people who loose weight find it hard to keep it off, as the body doesn't use up fat as well as others.

Another study showed that 50% of the fat uptaken by a cell is burned as energy when beta-adrenergic is injected nto forearm muscles. However people with type II diabetes none of the fat taken up by the cell was used in producing energy, thus the fat was stored in the muscle. It would appear that in insulin resistance that cells loose the ability to switch fuels from carbohydrate to fat burning. And this inability seems to continue even after weight loss in diabetics. This is why diabetics find it hard to loose weight, and keep weight off.

The question then flows - is it obesity that causes the muscles cells not to absorb fat? Or is it that cells not absorbing fat that makes people obese?

Data would seem to indicate that it is the cells not burning fat makes people obese. The Respiratory Quotient (RQ) looks at how much carbon dioxide you breath out, compared to the oxygen you breath in. This can tell what type of fuel your body is burning. RQ is 1.0 when you are burning carbohydrates, and is approximately 0.70 when you burn fat. A study looked RQ and risk of obesity at Pima Indians in Arizona. They found people with a higher RQ more likely to be obese than those with lower RQ. That is people who more likely to burn carbohydrates than fat, are more likely to be obese.

It also appears that it is not only the difference between between using fat or carbohydrates, but also from where the fat is taken from. The data is only preliminary, but would indicate obese people are more likely to use the fat in their muscles for their energy source than fat deposited in their fat deposits. Thus retaining fat in fat storage areas, which are the areas that people want to remove from their bodies.

So hopefully this removes some of the burden of struggling to reduce weight. And frees you from that negative self talk that beats you up about your inability to loose weight. Thus ultimately helping you to loose weight as you feel better about yourself.

Blaak. E., Basic disturbances in skeletal muscle fatty acid metabolism in obesity and type II diabetes mellitus, Proceedings of the nutrition society (2004) vol 63 pg 323-330 2004.

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