A neophyte guide to nutrition and fat loss

I have been reading about nutrition and fat loss topics on the Internet for a while, and the general sense is that there is a lot of confusing, sometimes contradicting information out there. So I had to figure out for myself the basics of nutrition, fat storage and fat loss, by reading first hand material from reliable sources – mainly Wikipedia, Encyclopedia Britannica, plus a number of research grade review articles.

This is the picture I came up with. It means to be as scientifically accurate as possible, but without getting too much into the scientific details (which can be really hairy!) – and without making it simplistic too.

Here is The Doctor’s guide to nutrition and fat loss, and its main takeaways.

The human body at rest

The body constantly needs energy – all the time, even at complete rest. The human brain, for one, is functioning all the time, and is a huge consumer of energy. But even at rest, the body is constantly performing many basic life functions, which all require energy. Consider, for instance:

Keeping the internal temperature at 37 C;
Digesting food;
Maintaining basic vital functions: breathing, heart beat, etc…

The Basal Metabolic Rate is the energy required to maintain these basic life functions at complete rest. For a physically untrained, normal adult man, it is around 1800 calories a day. And probably 15% less for an adult woman.

Note: In the context of this post, what I call one calorie is actually 1 Cal (large C) or 1000 cal (small c) or 1 kcal. One calorie represents 4187 Joules of energy. 2000 calories over a 24 hour period represents 97 Joules per second (also called Watts). The human body is a chemical plant generating about 100 Watts of power…

When you add daily physical activity to the picture, the energy requirements go up: 2200 to 2500 calories per day for a normally active adult man, or more. It is going also to depend on your body composition: one kilogram of muscle requires more energy to maintain than one kilogram of fat. A more muscular man can easily afford to eat 3000 calories each day before he even starts to gain weight!

Food: where the body gets the energy it needs

The food we consume ultimately comes down to three big categories of “macro-nutrients”:

Proteins

Proteins are large molecules made up of amino acids. In the body, they perform multiple essential functions.

They form an important component of the cells and cell membranes.
They provide important catalysts for the chemical reactions in the cells.
Also, they provide enzymes for digestion, antibodies, and hormones.
And in the last resort, the liver converted them into glucose for energy use.

Fats

Fats usually come up either as triglycerides (i.e. animal fats), an assembly of a glycerol molecule with three fatty acids, or directly as free fatty acids (in liquid oils).

They provide the building blocks required to build hormones and cell membrane.
The body uses them for energy storage: the “fat reserves”.
And they can directly provide energy to the body, though the oxidation of fatty acids.

Carbohydrates

You could define carbohydrates as “sugars” in the most general sense – even in the absence of “sweet” taste. Digestion breaks down carbohydrates into their elementary sugar components, the most common of which being glucose. The cells can directly turn glucose into energy, or store it as glycogen for future conversion into energy.

The digestion process consists in breaking down all these macro-nutrients into their smaller components (amino acids, glycerol, fatty acids, glucose and other simple sugars), and sending them to the cells via the bloodstream.

There is much more to nutrition

This simple picture didn’t take into account other important nutrients such as vitamins and minerals. But this post only considers nutrition from the point of view of energy production, consumption, and storage in the body.

How the cells produce energy

There are essentially two ways living cells generate energy.

Glucose catabolism

Glucose (from carbs) is the elementary sugar that can be directly used by the cell to generate energy. Within the cell, a glucose molecule undergoes a number of complex chemical reactions and processes:

Fatty Acids catabolism

Fatty acids (from fats) can also be used to generate energy. They undergo several rounds of “Beta oxidation”. These reactions generate intermediate products which then go through the same later stages as above, thus:

Beta oxidation
Citric acid cycle (or Krebs cycle)
Electron Transport Chain

In this context, “fat loss” essentially means turning some stored triglycerides (fats) into fatty acids, and sending these fatty acids to the cells via bloodstream. The cells will then oxidize glucose into energy as described here.

The description of these chemical processes goes beyond the scope of this post. But they are really hairy, complex chemical reactions, which forces us to wonder about the beauty of nature.

For our purpose, the net effect of these catabolic processes is that they eventually generate molecules of ATP.

The burning of one glucose molecule can produce up to 32 ATP molecules. The burning of one molecule of palmitic acid (one example of fatty acid) can produce up to 130 ATP molecules.

ATP: the energy currency of life

So the processes we described eventually generates molecules of ATP, (Adenosine TriPhosphate) which are complex molecules with high internal energy. The hydrolysis of ATP, a final chemical reaction which reduces ATP into ADP, eventually releases this energy. Finally, the above chemical processes will recycle these ADP molecules.

The release of the energy stored in ATP is what creates heat in the body, and what makes muscle cells to contract. The energy produced and consumed by the body is directly proportional to the number of ATP molecules produced.

You can consider that your body, in average, produces about its own weight in ATP molecules, every day, just to stay alive. That translates to about 100 millions ATP molecules produced each second, in each cell… That seems a lot! Until you remember that the resulting ADP molecules are recycled into ATP, then ADP, then ATP again, many, many times a day.

The fate of excess glucose

But say a molecule of glucose reaches a cell when energy is not immediately needed. What happens then?

The cell will attempt to store the excessive glucose molecule within the cell, as glycogen (an assembly of several glucose bound together), for later use. Glycogen thus represents the cells “sugar reserves”.

The body, however, has a limited ability to store glucose into glycogen. In total, it can store up to around 400 to 500 g of glycogen, or the equivalent of 2000 calories. This represents about one day worth of basal energy needs. The muscles have about 400 g of storage capacity, and the liver can store up to 100 g of glycogen. The glycogen stored in a given muscle is only available for the consumption of that particular muscle. The glycogen stored in the liver, however, is available for the whole body needs as required.

Now, if the glycogen stores are full, the cell will then pass on the excess glucose to the adipose cells (also called “fat cells”, because their function is to store fats). In turn, these cells will turn this glucose into triglycerides (i.e. fats).

That’s the main way we accumulate fats!

How about proteins?

Proteins are not directly used to derive energy. However, amino acids provide some intermediate chemicals which are used as inputs into the above mentioned reactions. So yes, they still indirectly contribute to energy production.

Plus, in the last resort, the body can turn them into glucose it can use as energy. In your body, the reserves of proteins are essentially your muscles!

The role of hormones

The hormones are the messengers in the body, released in the bloodstream when certain conditions are met. Their function is to instruct some target cells what they should do as a response. Now this is a very complex topic on which there are still some research going on. For our purpose, a few particular hormones play a role in regulating the availability of energy to the organism.

Insulin

Under normal circumstances, the nutrients present in the bloodstream cannot, by themselves penetrate inside the cells. To do so, they need to be enabled into the cells by a hormone called insulin. Insulin binds itself to a cell, after which the glucose and other nutrients are allowed to penetrate inside the cells.

The pancreas creates insulin when it detects a “fed state”. You will read everywhere that high glucose levels triggers insulin release. But the presence of amino acids (from the digestion of proteins) also do trigger insulin release, to a lower extent. (Digestion of fats, however, are neutral to insulin release.) That’s why I prefer to talk about a “fed state” rather than just glucose levels.

When the pancreas detects a “fed state”, it releases insulin in the bloodstream, which signals to the cells it’s time to feed. The amount of glucose and other nutrients in the blood goes down as the cells absorb them, after which the pancreas stops releasing insulin.

But what happens in a “fasted sate”, i.e. when the levels of glucose and amino acids in the blood are too low? With low insulin levels, the cells can’t feed! Yet, the body still requires about 2000 calories a day just to stay warm. That’s where glucagon comes into play.

Glucagon

Whenever blood sugar levels are low enough (i.e. in the fasted state), the pancreas releases the glucagon hormone in the bloodstream.

Glucagon induces liver cells to turn glycogen into glucose and release it in the bloodstream.

When the glycogen stores in the liver are depleted, glucagon then turns towards the body to create glucose from non carbohydrate sources, e.g. glycerol, lactate, amino acids. It also turns towards the adipose cells, and triggers the release of fatty acids out of triglycerides. These fatty acids can be used as energy source as described above.

As a result, insulin rises to the baseline level, and the cells can absorb nutrients again.

While insulin is the messenger that tells the cells to feed, glucagon is the messenger that tells the cells to generate glucose and fatty acids from stored sugars and stored fats, from nutrients other than carbs, and in the last resort, from muscles.

In essence, glucagon works towards increasing your blood glucose levels, while insulin works towards reducing your glucose levels. Insulin is what make your cells feed, but also store fats. Glucagon (among others) is what makes you burn fats.

Note that the same biological mechanism that promotes the release of insulin in the blood, is also inhibiting the release of glucagon.

The growth hormones

Essentially the Human Growth Hormone, and a related hormone called “IGF-1“. They are mainly released (i) during sleep, or (ii) when fasting, or (iii) during intense physical exercise. Their main purpose is to promote cell repair and cell growth. But they also trigger fat loss processes, by inducing adipose cells to release fatty acids out of stored fats.

The stress hormones

These are essentially adrenaline, nor-adrenaline, and cortisol. Their function is to mobilize the body for action, either in presence of stress or strong emotions (e.g. fear), or under vigorous physical exercise. They make the brain more alert, and senses heightened. They make the heart rate increase, the oxygen intake higher, the blood pressure higher. But they also support generation of energy source by the body – from glycogen stores, and from fat stores – in order to support the body for physical action.

Thus, growth hormones and stress hormones are the other hormones inducing fat burning, released notably during vigorous physical exercise, as well as during sleep and fasting (in the case of growth hormones).

What it means for dieting and fat loss

Sugars are stored into fats

Digestion directly turns carbohydrates into glucose, available for immediate consumption by the cells.

When they have no immediate need for it, the cells will attempt to store it as glycogen. But when the glycogen stores are full, the glucose molecules end up in the adipose cells. These cells will metabolize glucose into fats and store them.

Whereas the body can store up to 500 g of glycogen, it has no limits to the amount of fat it can store!

Fats can be stored into fats, but…

Adipose cells can absorb excess dietary fats present in the bloodstream, and store them as triglycerides. But insulin still needs to enable this absorption into the cells. Dietary fats are neutral when it comes to insulin / glucagon balance. So eating fats in itself can’t make you fat!

There has to be some carbohydrates, and to a smaller extent, proteins, in your food so that the pancreas detects a fed state and releases insulin, which in turn enables nutrient intake into the cells.

High insulin inhibits fat loss

As long as insulin is high, glucagon release is inhibited. At rest, the body can never tap into the fat reserves. However, in the presence of vigorous physical exercise, the body releases growth and stress hormones, which support the physical effort by triggering fat burning processes.

But that would happen only if the physical effort is high enough. Sprinting qualifies. But a moderate pace jogging doesn’t.

It is going to be very hard to lose weight under high insulin!

You must deplete your sugar reserves first

Our body looks for glycogen reserves in priority, before tapping into fats – as evidenced by the action of glucagon. If you are constantly operating at full 500 g sugar reserves, you have 2000 calories worth of glucose to burn before starting to tap into the stored fats. Good luck losing weight!

It is a little surprising that the body uses glucose as priority fuel and reserves: fats appear to be a much more efficient fuel source and storage mean than sugars.

Nature just never envisioned the kind of pervasive carbohydrates nutrition base as we have nowadays!

Fat loss occurs mostly in fasted state

You need a fasted state to release the fat burning hormones (glucagon and growth hormones). In a fed state, insulin is high which inhibits glucagon and fat loss.

If you are eating three main meals a day, plus possibly some snacks in between, you are keeping your body in a constant fed state, i.e. at high insulin levels. Your only fasting time will be during sleep – however a late evening snack will kill it off. In any case, this is simply not enough time to have significant fat burning happening. Remember that what will go in priority are the sugar reserves!

Conclusion. Dispelling a few fallacies

This study has been an eye opener for me, as it provided some scientific grounds to explain what I had personally observed in my life. The main conclusions are:

(i) our body was never designed to sustain such a carbohydrate-rich diet as we have today, and
(ii) we were never designed to be in a perpetual fed state.

It also helps to shed some light and dispel some of the biggest fallacies going around in “conventional nutrition advice”:

“I’m fat. I need to exercise regularly”

No, it’s not going to work, because you are likely sky high insulin all-day long, which inhibits your fat loss mechanisms. Vigorous regular exercise would help a bit, although you would still be running against your high sugar reserves. But moderate physical exercise will hardly produce any result.

What you need to worry instead is to lower your carbohydrates intake, as well as eating less frequently.

“Breakfast is the most important meal of the day”

No it’s not. When you are fasting you are depleting your sugar reserves, as well as triggering fat loss cell repair. You should aim to prolong the overnight fast a little longer, by skipping your breakfast! Just try it! It is surprisingly easy.

“I need a balanced diet with at least 45% of energy coming from carbohydrates”

No you don’t. That is going to provoke a massive insulin response. The excess glucose generated will eventually metabolize as fats. And the fat burning processes will be inhibited as long as your insulin remains high – which is likely all the time.

Such a non-sense notion is one of the root causes of obesity pandemic. For 99% of its existence mankind led a heart-disease-free life consuming much less carbohydrates than we do today.

I hope, dear Reader, that you have found this article as informative as I have! It was certainly an eye opener for me.

Yours,

The Doctor