Insulin and Leptin – very different effects in lean versus overweight people

The hormone  insulin  (involved in storing fat) and  leptin (involved in burning fat) work very differently in  lean people  than in  overweight people. This  is why excess fat such as is found  in “bullet proof coffee” or “fat bombs” results in overweight (or obese) people that follow a Low Carb High Fat diet gaining weight—whereas lean people will simply burn it off. This article explains the role of these hormones and how they impact lean people and overweight people very differently.

When we eat, the hormone insulin  is released which signals our body to do two things; (1) it tells  our cells to uptake energy (in the form of glucose) and (2) to store excess energy as fat.  Insulin  is the major driver of  weight gain.  If we are  lean, when we eat more than usual and increase our body fat stores, the body responds by increasing secretion of a hormone called  leptin.  Leptin acts as a  negative feedback loop  on the hypothalamus area of our brain, reducing our hunger, causing us to eat less and preventing us from  gaining  too much fat.

The problem occurs when we become  insulin resistant.

Insulin Resistance

When we eat  a diet that is high in carbs  and we eat every few hours  (3 meals plus snacks), insulin  is released each time we eat (in order to cause our cells to take in energy and store the excess as fat).  If  we continue to eat this way, over time our body is inundated with insulin, so it sends signals to  down-regulate the  insulin receptors,  making our cells  less sensitive to insulin signals. This is  called  insulin resistance. When we are insulin resistant, our  body releases  more and more insulin  to deal with the  same amount  of glucose in the blood.

Leptin Resistance

Consistently having high levels of  insulin, will also keep stimulating the release of leptin, which normally results in us becoming less hungry and eating less. However, when we are  insulin resistant,  we keep producing more and more insulin, which results in us  producing more and more  leptin.  Over time, this consistently  high leptin level  will result in the same type of down-regulation of hormonal receptors that occurred with insulin, resulting in  leptin resistance.

Leptin resistance  interferes with the negative feed back loop on our hypothalamus which normally reduces  our hunger, causing us to eat less. When we are leptin resistance, even when we’ve eaten a great deal of  food, we don’t feel satiated — even when our abdomens are straining from feeling full. As a result, we just keep eating, as if there is no “off” switch.

It is this  leptin resistance  that results in  obesity.

Obese people aren’t obese because they lack will-power, but because their body is responding to signals from very powerful hormones produced in response to the  types of foods  they eat.

Difference between a High Carb Diet and a High Fat Diet

When people consume  diets high in carbs it stimulates insulin  to be released.  In response to all the insulin, energy that is not immediately needed for activity is stored as  glycogen  in the liver and muscle cells, and the remainder is shipped off to our  adipose cells  (fat cells), to be stored as  fat.  When eating a high carb diet, getting excess calories into  fat cells is easy, getting the fat  out  of fat cells, not so much.

When people eat a  diet high in fat  and  low in carbs, the fat  is absorbed in the intestines as chylomicrons and is shuttled through the  lymphatic system to the thoracic duct, going directly into the blood circulation. From there, the fat is either burned for energy or  goes into our  fat cells, to be stored. It is important to note that the fat does NOT  go to the portal circulation of the liver and as a result,  fat needs no help from  insulin  to be absorbed.

That’s good, but if excess fat gets stored in fat cells, doesn’t eating fat make one fat?

Not for lean people, because lean  people are  leptin sensitive and  obese people  are  leptin resistant.  When  overweight or obese people eat excess fat, it is a different matter.

Lean People versus Obese People

If a  lean  person eats a diet high in fat and low in carbs, the excess fat will be stored in fat cells, but  insulin  does not go up. So a lean person does not become insulin resistant, as described above.  As their  fat mass goes up,  leptin  also goes up.  Since the lean person is sensitive to leptin, the negative feedback loop acts on the  brain causing them  to stop eating, allowing their body weight to go back down.  Even if a lean person deliberately eats more and more fat when they aren’t hungry, what happens is their body’s  metabolism goes up,  and they  burn off the extra calories.

If an  overweight or obese person  eats a diet  high in fat and  low in carbs  with moderate amounts of protein, insulin levels don’t go up — which is good of course, however from years of eating  high carb low fat diets  and from eating a  carb rich foods every few hours, overweight and obese people are  insulin resistant. This means that  their  blood glucose levels  remain high for long periods after they’ve eaten and as importantly, it also means that they are also  leptin resistant.  In this case, if they eat  too much fat  – such as drinking “bullet-proof coffee” or having “fat bombs”,  they will  respond (as the lean person does) by  making more leptin,  but the problem is,  they are  not  sensitive to leptin! Their brain doesn’t respond to the signals from leptin, so when an obese or overweight person eats excess fat, beyond that which is naturally found in a low carb high fat foods,  their appetite doesn’t drop  –  nor does their metabolism go up  to burn off the excess fat being stored in fat cells. They simply get fatter.

Weight Loss

For those that are overweight or obese and  insulin resistant, it is important to keep in mind that with  insulin resistance comes  leptin  resistance. Leptin resistance by definition means that  the signals to  stop eating don’t work.  The “off switch” is defective.  As well, the body doesn’t respond to signals from leptin to  up-regulate metabolism, so when an overweight or obese person on a low carb diet eats too much fat, they gain weight.

Since increasing carbs is not an option and increasing protein results in glucose being synthesized from the excess (gluconeogenesis), the way to lower insulin resistance (and thus leptin resistance) is by extending the amount of time between meals.  This is known as intermittent fasting – a topic that will be covered in a future article.

Have questions?

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To our good health!


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