Why we get FAT? – Part 2

If you have not read Part 1, please go there first.

This part will provide a general overview of what happens before and after we consume food or drink. The format of this post is more Q&A style covering a number of common questions and myths.

The digestion and assimilation of food in humans is a wide ranging and complex topic and I am no expert in this area. I will focus on the aspects that are relevant for our discussion and keep it at a high level.

Some basics first

  1. Various tissues and organs in the human body need energy on a continuous basis to  execute their functions (heart, lungs, brain etc.). The common denominator or currency for energy is ATP
  2. The most abundant form of energy supply in the body is in the form of Glucose which is supplied by the Blood to the tissues and organs (also commonly called Blood Sugar)
  3. In general, humans consume three categories of food items (called “macro-nutrients”) – Carbohydrates, Fat and Protein. (Vitamins and minerals are “micro-nutrients”)
  4. Glucose is a form of Carbohydrate and when we eat food containing easily digestible  Carbohydrates (sugars, white flour etc.) this gets converted into Glucose in the blood relatively quickly
  5. Body can convert Fat and Protein into energy as well but some organs like brain have a strong preference for Glucose

How is energy stored in the body?

There can only be limited amount of energy available in the blood circulation as the body tends to maintain the glucose levels in the blood in a reasonably narrow range. Too much sugar in the blood has a lot of side effects and hence glucose levels are maintained tightly in the blood and this is ensured by Insulin. As soon as there is glucose in the blood (after food intake), Insulin (a hormone) gets secreted at a higher level.

Insulin is secreted in the Pancreas in very small quantities but it is extremely potent and can potentially overpower many other hormones. Insulin has many functions but its primary role is energy storage. It is a storage hormone.

There are two forms of (energy) storage in the body just like in a PC – a limited but quick form (like a RAM in a PC) called Glycogen and a larger, more permanent form (like a hard disk in a PC) called Fat (also called Adipose Tissue).

Once the blood sugar levels go beyond a range, Insulin will start to provide the Glucose to the liver and the muscle to store it in the form of Glycogen (think of Glycogen as an aggregated form (technically it is a polysaccharide (many sugar molecules clubbed together) of Glucose and water). There can only a limited amount of Glycogen in the body (approx 100 to 200 ml or so in Liver and perhaps 200-300 ml in other parts – mostly muscle).

If there is still lot of Glucose in the blood even after providing Glycogen, then Insulin will start pumping this into Fat cells and it is stored as Fat (these two processes may happen simultaneously and not necessarily sequentially). The level of Insulin (which is determined by the level of Blood glucose in a healthy adult) determines how much fat is stored.

More Blood glucose means more Insulin means more Fat. This is a fundamental point to be remembered.

Because the Glucose is a) getting used by the body b) being stored as Glycogen and c) getting stored as fat, naturally the Blood glucose level falls to the normal range a few hours after a meal, by which time the Insulin level falls down (in a healthy adult) (because there is nothing much for the Insulin to do any longer).

How does the body run when the Blood Glucose levels continue to fall down?

As we have seen earlier, body would like to maintain a constant supply of energy (within a range). When the blood glucose levels fall down a certain level (due to consumption of energy by the tissues which will reduce the amount of glucose in the blood), Liver will provide energy from the Glycogen reserves and fats from Fat tissue will start to be broken down into free fatty acids which go into the cells and are then broken down to provide energy.

Crucially, it appears that supply of energy from Glycogen (the temporary, quick storage) and Fats (the more permanent storage) can only occur if the Insulin levels are very low. So to break down the Fat in the body, we need to keep Insulin levels low which implies keeping blood sugars low (there is a role for protein and we will discuss that later in this post).

When and why do I feel hungry?

When blood sugar come down to a lower level and Glycogen stores starts to get depleted, hunger signals are generated in the body and some special hormones (particularly one called “Ghrelin”) gets produced. The job of Ghrelin is to make you hungry so that you can go around looking for food.

The processes related to energy supply and hunger seem to work differently at day than at night and that is why we don’t go looking for food in the middle of the night even though our last meal was more than 5-6 hours ago. We seem to do that during the day. The hormonal cycle may behave differently at night. It it also the case that energy consumption is low at night but this does not fully explain being without food for 12 hours or so.

When do I stop consuming food?

Another hormone called “Leptin” gets produced in the body when we start eating food and the level of Leptin slowly rises. Leptin receptors in the brain start monitoring the level of Leptin and once it reaches a certain level, a signal of Satiety (fullness) is apparently sent which makes you stop eating. (It is speculated that Leptin signals are sent quickly if you consume a food rich in fats and proteins as compared to Carbs meaning fullness is reached quicker with fatty foods or meats/dairy products etc.)

As a slight anecdote, people have run medical trials where the participants have been asked to only eat Fat and Protein but can eat as much as they like. Apparently many of them struggled to eat more than 2,500 to 3,000 calories because they felt full relatively easily.

So, the body ensures that there are strong checks and balances and controls so that the processes work in a reasonably tight range and most of the time they do work properly.

Can you please run the sequence of events past me again?

  1. Your blood glucose levels are running low
  2. Body produces Ghrelin (and perhaps others) which makes you hungry
  3. You go looking for food and start eating (let’s say it is mostly Carbs)
  4. Insulin secretion starts
  5. While there is Insulin in the blood, liver will stop providing Glycogen and break-down of Fats for energy stops (this happens for a good reason – the logic goes like this – why break down energy reserves in the body when we are getting additional supply of energy by means of food)
  6. When there is sufficient food, Leptin signals that you had enough. You stop eating.
  7. Carbs are digested and enter the circulation as glucose.
  8. Blood sugar levels increase
  9. More insulin is secreted
  10. Glycogen stores are topped up
  11. Blood glucose and Fats in the Diet are pumped into the Fat Cells by Insulin
  12. The levels of Fat increase
  13. Over a period of time, the blood sugar levels go down and Insulin levels go down
  14. Body will then starts releasing Glycogen and Fat for energy
  15. Once Glycogen stores go low and blood sugars go low you will feel hungry
  16. The cycle starts again

The picture below (courtesy: stargazey) shows how energy is supplied to the body after a meal (or glucose in this instance) (Gluconeogenesis below refers to body’s way of generating glucose from various sources)

Gluconeogenesis--Time Course

If the Carb levels are high, the blood sugar levels are high which means Insulin is high which means fat storage is very high.

This all sounds normal, so what is the problem?

If the blood sugar levels are high only temporarily or once in a while that’s correct. Also if you are young you may be able to cope.

If your blood sugar levels continue to be chronically high (over a long period), then Pancreas will try to respond by secreting more and more Insulin. Initially the tissues and liver respond fine, but over a period of time higher Insulin levels no longer produce the desired effect and blood sugar levels continue to stay high. The response would be more Insulin from Pancreas. There reaches a point when the additional Insulin is not able to reduce the Glucose levels in blood sufficiently. This is called “Insulin Resistance”. This is the first stage for what is known as Metabolic Syndrome or Syndrome X – in layman’s terms this is pre-diabetes.

What is wrong with having high blood sugar levels?

The pre-diabetic condition with high blood sugar levels start harming the body in a number of ways and is meant to precipitate High Blood pressure, Stroke, Heart Disease, Cancer as well diseases related to Kidneys, Eyes, Diabetic Neuropathy (leading to amuptations) etc. Diabetes is known as a Silent killer. It will start damaging a number of organs of the body.

Also high blood sugar levels are meant to promote Inflammation (we will discuss this later in another post) which is responsible for the blockages of arteries etc. It is also well known that cancerous tissues need a lot of sugar to grow (and cancer is out of control or abnormal growth of cells) and there is one theory that higher blood sugar levels make things worse for caner (whether some cancers are caused by the high sugars in the blood is a topic of controversy).

Higher blood sugar levels generate a lot of products in the body which are harmful – examples like AGE (Advanced Glycation End products etc.)

Sometimes I don’t stop eating when I should. Why?

As discussed earlier, the signal to stop eating comes from Leptin (amongst other things). It appears that when we eat a meal containing sugars and Carbs, body produces fatty components called Tri-glycerides (we will discuss more about this in the next post about Cholesterol but Tri-glycerides are the form of fat in our body – mostly). If the Tri-glycerides are produced in the normal range then it seems to be ok, but if the Tri-glyceride levels are very high they seem to interfere with the Leptin signalling and the brain does not respond in  time for us to stop eating. This inability of Leptin to generate the “Stop Eating” signal is known as “Leptin Resistance”. Apparently “Leptin Resistance” is also common when you consume a lot of fruit juices, sugary drinks (like Coke – even if it is Diet Coke etc.) i.e. too much Fructose or Sugar.

So, once again – try to stay away from anything that tastes SWEET as much as possible no matter it is Diet or low-cal or Fruit based.

Will only Carbohydrates and Sugars raise Insulin levels?

Not really. Insulin also helps break down protein and to that extent Insulin is secreted when you eat Protein. The only macro-nutrient that does not generate a decent Insulin response is Dietary Fat (Fat in the meats, Dairy products like cheese, Eggs, Fish, Oils, Butter etc.)

So in a sense the worst combination of food (after a food containing only Carbs/Sugars) for someone who is Insulin Resistant would be a diet containing Carbs and Protein only with no Fat (e.g. Lamb Biryani or Chicken Fried Rice)

It appears that Dietary Fat moderates the Insulin response.

But I was told that you have to eat Carbs for energy. Is that not correct?

As discussed earlier in the post, human body is smart enough to convert any of the macro-nutrients (Carbs, Fat or Protein) into energy. Theoretically, you do not have to eat Carbs to live and you certainly do not have to eat a single gram of sugar in your entire life to live normally.

On a practical level, some Carbs (for taste, variety, practicality, availability etc.) are perhaps needed. But the average consumption of Carbs is at the high end for most people these days.

I feel hungry or crave for sugars (chocs etc.) 3 or 4 hours after a normal meal. Why?

I guess it depends on the word “normal”. If by normal you mean 200-300 gms of Carbs/Sugars and some Protein and Fat, then that is not “normal” according to my definition.

If you eat a lot of rice or a significant amount of bread (as sandwiches etc.) then your blood sugars go high. Body responds by producing a large amount of Insulin and most of the Glucose is pumped into fat and sufficient amount of Glycogen is not produced. So after 3 or 4 hours your body is starving for energy. In the normal course, the fat is released as fatty acids and all is fine but if the Insulin levels are high (because you may be Insulin Resistant) then fat does not get released. So you will be in this ironic state when your muscles and tissues do not get enough energy (water, water everywhere but not much to drink) and you will feel tired and fatigued.

So I regularly see people in my office raiding the vending machine between 3 and 4 pm.

You can easily try this out. Do this on 2 separate days and make a note (mentally or on paper).

Day 1 – Have your lunch with just Carbs and Sugars (cakes, juices, chocolates etc.). Make a note of how you feel 3 to 5 hours after a meal (I guarantee you will feel hungry despite the amount of food and energy intake)

Day 2 – Eat mostly Fatty foods and protein with very little Carbs (less than 20 gms). See how you feel 3 to 5 hours (I bet that you would still feel heavy in your stomach and not hungry).

If you want to know some technical detail, there is something known as “Reactive Hypoglycemia” (Hypo is low). This means “low blood sugar”.  Pls see the picture below



This shows the Glucose levels for different types of conditions. The normal level is between 4.5 and 5.5. You can see that under two of the conditions (Prediabetic and Hypoglycemic) the blood sugar rises rapidly (but not as much as in a diabetic) and then undershoots and goes below the normal level. This is why you feel cravings and tiredness.

What about Alchohol?

Alcohol works slightly differently. It is mostly metabolised by the liver and to that extent any excessive alcohol intake has the potential to do harm to the liver. Also each gram of Alcohol has approximately 4 calories. Together with a heavy load of Fructose (either via sugars or sugary drinks or too much fruit) the load on the liver could be considerable. Please pay attention to what you are eating/drinking while taking alcohol.

I read that – once I put on Fat, the Fat cells do not grow smaller?

Previous research indicated that a given person is born with a certain number of fat cells and the only thing that changes is the size of each cell. Current research seem to cast doubt on it, but it does seem likely that some message is passed on down to the babies when they are in the mother’s womb. There are a lot of studies out there that indicate that babies born of Fat mothers and Insulin Resistant mothers tend to be fatter in the long run. This is supposed to be caused by the high blood sugar levels in the mother during pregnancy.

Also, contrary to popular belief, Fat is not something which just goes and sits in the Fat cells. It is not inert. Fat tissue is metabolically active. Fat keeps moving IN and OUT of the Fat tissue continuously.

continued in part 3

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