Why are some people slim, apparently regardless of what they eat?

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Some people that come to me for a biosignature consultation are already fairly slim, regardless of age or activity level.  They could lose a stone or so, but even at their current weight they are far from unhealthy.  Others come in and clearly we are in for the long haul to get them down to a desirable body fat.  This blog is going to examine some differences between the slim and the fat.

Now, the biosignature involves taking 12 body fat measurements, and the one of greatest interest here is the one just below the shoulder blade which shows genetically how well the individual tolerates carbohydrates1.  It also shows the individual’s propensity for heart attacks and diabetes.  What I always find is those with a low fat reading here are reasonably slim already – and when I question them closely about their food intake I find that they generally have a very good relationship with food.  They eat well, and usually swear they eat a lot of food.  However, on pressing I actually find that what they rarely do is overeat.

I also find that people with a low shoulder blade reading are in the minority, meaning that most people are what Charles Poliquin calls carbohydrate intolerant.  This means that when they eat a high carbohydrate diet, they will gain body fat.  The reasons why are complex, one of them being how their bodys handle those carbs.  Someone who is carbodydrate tolerant will handle sugars much more effectively, because their insulin, the fat storage hormone, is more efficient at returning blood sugar levels to normal.2

The above video starts with Dr Philipp Scherer, University of Texas talking about body fat.  Body fat is made of fat cells that fill with oil as we eat more than we need.  Eventually the fat cell is totally full, so the body manufactures more fat cells.  There are certain times in life when the body is more prone this manufacturing of more fat cells than others – and one of those times is childhood.  Once the fat cell exists, its job is to accumulate as much fat as possible, encouraging us to eat and eat.  The volunteers that took part in this study for the programme were all slim as children.  So one reason why people remain slim throughout adulthood is because they were slim as children, so have less fat cells driving them to overeat.

This BBC programme is very interesting, and one of the things it showed is that a couple of the volunteers had a great deal of difficulty reaching the set daily calorie target – they both just could not eat that much food.  If they did, they vomited it up.  And this will be due to the production of Leptin3.  Leptin is the homone of satiety signalling that we have had enough to eat.  There is more on this in the page Why weight loss can be so difficult.  As we get fatter, we get leptin resistant, so no longer hear its signals to stop eating.

In the final programme, the programme looks at the work of Dr Rudy Liebel of Columbia University who has been studying a group of obese people in his laboratory.  After following a starvation diet, in which they lost 10% of their body fat, these people were then fed the exact calorie needs for their body weight and they all reported feeling persistently hungry, leading to the conclusion that the body tries to keep us at the same level of body fat, referred to as the fat set point.  However, there are also things to bear in mind such as the walls of the fat cells getting hard, so nutrients can’t get in or out, leading to malnutrition. So it is also possible that these obese people were feeling hungry because their body was crying out for proper nutrition.

The experiment found that a couple of the volunteers did not gain much weight and this was put down to more fidgetting.  One of my clients has 2 children, one slim and the other prone to weight gain.  The slim one is always active in a fidgety kind of way, whereas the child with the chubby tendency will lie for hours on the sofa watching TV or playing with computer games, etc – unless stirred up by his mother, of course. So another reason for slim people staying slim is that they just move about more – jiggling their foot, hopping up to do something etc.

One subject not covered by the programme is stress handling.  Stress causes us to put fat around the navel area – for ready access.  Now for some people, the response for stress is to reach for comfort food; chocolate biscuits, fudge, crisps et al.  But not everybody responds to stress in this way.  Officially 2/3 of people eat more food as response to stress and 1/3 eat less.  Why this should be so is very complex.  In the wonderful book, ‘Why Zebras Don’t Get Ulcers’, Robert Sapolsky posits that not everybody secretes as much of the stress hormone involved, that some people’s livers are “pokier” at breaking it down, and that part of the reason is due to individual attitudes towards food.  It really is not a good idea to use food as an incentive or as a comfort with children since this will set up precisely this response.

I feel certain that there are other differences between the naturally slim and those who fight the battle of the bulge.  But this little list goes some way to explaining things.  Essentially the slim do not overeat, they do not comfort eat, they move about more, they handle carbs well and they were slim as children.   However, just because someone is slim does not equate to them being healthy.


  1. these are the sugars, starches, fruits and vegetables []
  2. On 20th September, 2011 in the Daily Mail there is an article about the obese and hunger being triggered by slight drops in glucose. []
  3. Power C, Miller SK, Alpert PT.  Promising new causal explanations for obesity and obesity-related diseases”  Biol Res Nurs 2007;8;223.  DOI: 10.1177/109980040629674 []

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