THERMOGENESIS - what it actually means, and why it is important for those wanting to lose weight!

This is the first of a series of Newsletters intended to explain the basic science underlying the nutrition of weight loss in simple user-friendly language.

Thermogenesis became a “buzz” word some 10 or 15 years ago, and though it is superficially a simple concept, it is much more complicated in reality. There are not many who really understand what it is, and what it can do for those who want to lose weight. The reason for this may be that the term “thermogenic” has been arbitrarily and often unjustifiably used by many purveyors of diet products who, from lack of knowledge of what their products do (or maybe because their products do not actually do anything!), simply gloss over the lack of basis by calling their products thermogenic.

The simplest definition of thermogenesis is “generation of heat” (from the Greek words for heat and origin). If we add on to that “especially in an animal body by physiological or biochemical processes” we are much closer to what it means in the human body. Replace the word “heat” by “energy” and change it a little to give “generation of extra energy in the human body, brought about by physiological processes”, and we are close to the mark.

The body uses energy continuously to maintain body temperature and the host of physiological processes that occur in all cells and tissues and which keep us alive. We do not refer to that energy as thermogenesis, though it is generated by other physiological processes which take the breakdown products from the food we eat, oxidize them, directly or indirectly, using oxygen in the air we breath, and turn them into molecules with high energy content that can pass that energy content on to other processes which need energy to drive them. This can basically be viewed as burning the food at low temperature so that instead of immediately releasing carbon dioxide and water into the atmosphere (as would happen, for example, if you burnt the food in a fire), the energy is stored for a short time so it can be used in a regulated fashion and only slowly releases the carbon dioxide and water. This energy that is continuously generated and used, even though it could be described as thermogenesis (since it is the generation of energy from “fuel”), is referred to as “resting metabolism” and we often refer to the base state of our metabolism, when everything is just ticking over, as basal metabolism or resting metabolism. The level of this activity is then referred to as “resting metabolic rate”, or abbreviated as RMR, and it is the minimal amount of energy required to maintain vital functions. Normally, we would then calculate the energy costs of the various activities we perform routinely each day, and add them on to obtain a figure for our net energy requirement per day. This is an important figure, because it tells us how many calories we can eat each day without either gaining or losing weight.

We start talking about thermogenesis when we see an increase in the RMR that is related to something we have eaten, or something that we have done.

As you will have seen from the last few sentences above, we always need a few hundred calories per day over and above our RMR to cover normal activities, and though those activities are indeed “something that we have done”, we do not normally count them as thermogenic, though in fact exercise is indeed thermogenic, and our normal daily activities do count as exercise even if they are pretty minimal!.

What happens when we eat is a good example of why the body needs some extra energy. The food we eat contains complex molecules that have to be broken down before we can absorb them. So the body has firstly to perform work in order to secrete the digestive juices; basically, whether we talk about saliva, gastric juice, duodenal juice or the digestive juices in the rest of the intestinal system, we are talking about water containing electrolytes (such as sodium and chloride ions), proteins (the enzymes) and some other factors the enzymes need to work. Though this secretion of digestive juices goes on all the time at a low level, it speeds up when we put food in our mouth. Then more energy has to be put into the actual digestive processes; the enzymes which break these complex molecules down need energy to break the chemical bonds in the large molecules and turn them into smaller molecules, such as sugars (from starch) and amino-acids (from proteins) that can be absorbed.

In most cases, the act of absorbing these small molecules through the walls of the digestive system also requires energy. And finally, these small molecules have to be “processed” in the liver and other tissues to extract the energy from them, or to convert them into substances that help maintain the structure and function of the body in other ways.

So to extract the energy and nutrients from the food we eat, the body has to invest some extra energy into converting the food into a usable form. You could compare it with the process of converting a barrel of oil (the sort that comes out of oil wells) into gasoline; the oil is “cracked” at high temperature in tall towers in order to convert it into a form that can be used to fuel our cars. In other words, you put some energy in so you can get more out!

The thermogenesis that occurs when we eat is just like that. You have to put some energy in to get more out. We call this energy that we put in the “thermic effect of food” or “dietary thermogenesis”, and it is triggered by eating, digesting, absorbing and finally metabolizing the food.

Our weight problems, and the gradual increase in obesity throughout the world, are mainly due to the fact that some people (in fact, at least half the population), are pretty efficient at converting food eaten into usable small molecules (call them metabolic substrates) inside the body. They do not need to invest a lot of energy to get a lot of energy out, and these are the people who tend to “put weight on” easily. Others generate a lot of energy when they eat, and they tend to remain thin.

We speak of the first group, those who tend to put weight on, as having defective thermogenesis. That implies that there is something wrong with them. In fact, there is nothing wrong with them, they simply carry a genetic burden that once was an advantage, but is not so now in our modern society.

Their metabolism has been genetically “fine-tuned” to run more efficiently, so they can store more of the calories in food! In other words, if you have a tendency to be fat, it is a consequence of genetics!

Our remote ancestors faced harsh conditions for survival; even at the end of the last Ice Age, life expectancy was short, and many may not have lived past their 20^th year. Cold climates and times of famine meant that Nature selected those who were best able to survive, those who had sufficient stores of fat to resist the cold and get through times of food shortage.

The ability to store fat became a positive survival trait, and those who carried the genes that enabled them to convert food into fat more efficiently lived longer, reproduced more, and passed those genes on until now they are present in at least 50% of the human race.

Even in historical times, and until very recently in undeveloped countries, fatness has been considered a virtue, contributing to survival of the species. Nowadays, of course, being fat is only rarely an advantage! We now know that being fat kills, but why did we only really become aware of this during the last 60 or 70 years?

Historically, obesity, unless massive enough to completely impair function, was never treated; it was not considered a threat to survival, and in fact was often desired as an indicator of high social status. There were many other diseases that killed at an early age, mainly infectious diseases such as tuberculosis, smallpox, plague, not to mention the risks associated with accidents and surgery, and people just did not live long enough to die from the “diseases of civilization” of which obesity is the cornerstone! Our remote ancestors, to whom having large stores of fat was an advantage, had very short life expectancies. They died young because of accidents and infectious diseases. No emergency rooms, no doctors, no antibiotics!

During the Roman Empire, Romans had an approximate life expectancy of 22 to 25 years. But life expectancy rose rapidly in the 20^th century due to improvements in public health, nutrition and medicine (though in nutrition we slipped a little in the middle of the century).

In the United States, a new-born baby born in 2004 has a life expectancy of nearly 78 years; in 1973, that was 71 years, while in 1902 it was only 49 years!

So now we live long enough to suffer from the consequences of obesity! And now we know that “defective thermogenesis”, once a valued virtue, is making us fat and killing us.

So what can we do about that?

The answer is, when we try to lose weight, first make sure our metabolism is in an optimal state (no hidden deficiencies of vitamins, minerals or essential fatty acids), then increase our thermic response to food by deliberately choosing foods which maximize thermogenesis, and if necessary, improve on this by using Dietary Supplements which have proven thermogenic actions or doing other things that increase thermogenesis.

Starting with food, as we have seen above, the body responds to intake of major nutrients by imposing a sort of handling charge, which is the energy the metabolism must generate to cover the cost of digesting, absorbing, breaking down and rebuilding the nutrients.

It can be quite significant; for example, protein in adequate quantities can increase the RMR by 10% - 20%, even in individuals with defective thermogenesis. The increase is rather less for fat, and least for carbohydrate.

This is just one of the reasons why good diets are based on adequate protein intake (there are other reasons, which will be dealt with in another Newsletter).

Adding in a thermogenic Dietary Supplement can add another 5% or more to the thermogenic effect of the protein. The figure shows the additive effects on thermogenic response in the same obese volunteers given a protein meal, then one week later given the protein meal together with a Bitter Orange extract.

The protein meal consisted of two bars totaling 30 g of protein. That by itself increased the metabolic rate by 13.8%. Giving 35 mg of mixed citrus alkaloids from Bitter Orange added 4.5% to the increase in metabolic rate. In both cases, the metabolic rate remained above baseline for nearly 6 hours, which is significant, because it means that any further food that would have been consumed during that time would also have been going into a system where the metabolism was increased, and the net caloric value (in other words, the energy available for storage as fat) would have been reduced.

To paraphrase in simple terms, creating a hotter fire burns more calories, and results in better rates of weight loss!

So how does all this relate to efforts to lose weight? In simple terms, overweight patients are put on diets to create energy deficits, so that, to obtain the necessary energy to cover their basal metabolic requirements (keeping the body running; RMR) and their daily activities, they have to burn off their surplus fat.

Unfortunately, most of those who need to lose weight have a poor thermogenic response to food. In addition, if energy intake is simply reduced by doing nothing more than eating less, the body also adapts to this "time of famine"; the metabolic rate gradually falls and the body tries to preserve its not-so-secret stores of energy reserves as long as possible.

Even those with “defective thermogenesis” will, however, respond to the consumption of thermogenic substances such as protein and Bitter Orange. Furthermore, using a low calorie thermogenic diet also can prevent the fall in metabolic rate that would otherwise occur, and will help achieve the objective of “burning off” the stored fat.

This Newsletter would not be complete without mentioning other ways of increasing thermogenesis, and giving those who want a more scientific explanation a little “food for thought”.

As noted, making the body perform extra work is thermogenic. So exercise is thermogenic, and it does not need to be exhaustive, simply walking a couple of miles 2 or 3 times a week is adequate but not so intense that it increases appetite (counter-productive!). Decreasing the temperature of the environment also makes the body work harder (to maintain body temperature). Even drinking those 8 glasses of water a day makes the body work a little harder and burn more calories (though there are other reasons why you need to remain hydrated when on a diet).

And what is the basic mechanism of thermogenesis? That can be explained by the figure below.

Everything you do to increase thermogenesis has a positive impact at a cellular level. The hormone noradrenaline (NA; norepinephrine), or, for example, some of the citrus alkaloids from Bitter Orange, can activate what we call beta-3-receptors on so-called effector cells. These latter may be fat cells, or muscle cells, or even cells in other tissues.

This causes one of the high-energy substances we mentioned before, cyclic adenosine monophosphate (just call it cAMP), to be released in the effector cell and that in turn increases the rates of a number of metabolic processes in the cell. Bingo, increase in metabolic rate!

Protein, of course, contains essential amino acids, two of which, tyrosine and phenylalanine, are precursors in the body for noradrenaline, so no real coincidence that protein is thermogenic, though that is not the only reason it is thermogenic. Essential fatty acids, in the right proportions (of omega-6 to omega-3) also play a role, as do quite a number of minor constituents of food such as spices, caffeine and nicotine (yes, nicotine is thermogenic, and it does occur in a number of plants and vegetables other than the tobacco plant). Plus, of course, we make use of some of these thermogenic substances in rather more targeted ways in designing effective thermogenic Dietary Supplements. Specifically, to increase thermogenesis by giving a Dietary Supplement, we firstly make sure the essential fatty acid status is optimal (proportions and amount), then we use something like Bitter Orange that can increase release of noradrenaline and also activate effector cells directly. After that, we might use a herb containing caffeine to delay the enzymatic breakdown of cAMP (we need cAMP to remain effective as long as possible). Or we might use capsaicin, the active principle of some hot spices, which can also activate the effector cells.

Lots of “food for thought” there. And this “food for thought” not only contains no calories, but by making you think hard, actually causes the brain to use a few more calories than normal!

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