It’s popular to talk about certain foods that
stimulate thermogenesis, or heat production, as a means to aid in weight loss –
the most fashionable of which is probably coconut oil. While
that’s all good and desirable, the heat generated upon eating makes a
relatively small contribution when compared to all the heat generated by all
the reactions in the body, including the process of keeping the gut in a state
of continuous readiness to digest and assimilate the next meal.
All metabolic processes in the body generate heat. In other words, metabolism is unavoidably
heat-generating. The minimum amount of
heat generation is set by the resting metabolic rate,[*] which
is, in turn, set by the thyroid hormone, among other ancillary factors. The heat generated from eating – directly related
to the energy costs of digesting, absorbing, and converting the myriad of
components of food into their appropriate storage forms – adds to the heat
generated by the resting metabolic rate.
As far as diet-related heat generation is concerned, of all the
macronutrients, protein has the greatest effect. Carbohydrate has a lesser effect than protein,
and fat has a negligible effect.
Eating can also activate uncoupling proteins, whose
function is to process nutrients for heat rather than energy in the
mitochondria. Although the extent to
which this adds to heat generation is probably minor, the intensity with which
these uncoupling proteins generate heat is governed and fine-tuned by hormones,
in particular thyroid hormone and noradrenalin.1 Uncoupling helps to decrease oxidative stress, while
maintaining a high rate of ATP generation – an example of a substrate cycle in
which a substance (in this case a proton gradient across the inner
mitochondrial membrane) is generated and subsequently dissipated, in a reverse
reaction using different enzymes, wasting energy in the process.2
Although fat has a negligible effect in terms of
increasing heat generation after eating, it does play an important role in regulating
body temperature, as one of the myriad of reactions mentioned above not
involved with eating. This reaction, in
which fat is used to generate heat, is another example of a substrate cycle. In essence, triacylglycerol, composed of 3
fatty acids and 1 glycerol, is broken down (lipolysis) and the fatty acids subsequently
released are taken back up by the releasing fat cell and esterified into
triacylglycerol therein.[†] This process, lipolysis and esterification,
constitutes one substrate cycle, and the heat generated from the reactions in said
cycle plays an even greater role in regulating body temperature than the
physical role of fat as an insulator! Like
the uncoupling proteins, this substrate cycle is regulated by thyroid hormone
and noradrenaline.
At least on the order of days, weeks, or even
months, the addition of a particular food into a person’s diet in the absence
of other changes will probably not have a significant effect in terms of changing
a person’s body fat and weight. A case
in point is MCT oil, which has been promoted hard for its ability to aid in
weight loss. The results of clinical
studies in which MCT oil was put up against a different oil and weight changes
were tracked over time have been overwhelmingly unimpressive to say the least. Yet, a value to which it is not legitimately
entitled continues to be placed on MCT oil by the likes of Dave Asprey and the atrocity
that is the Bulletproof Diet.
However, the effects of changing the composition of
the fats in a person’s diet are not as ineffectual as I may have indicated
above. Interesting are the experiments
in which behavioral changes are observed upon changing the fatty acid
composition of the diet of an animal kept in captivity. Lizards, for instance, will become more
active at night and prefer to spend more time in colder places so their bodies
become colder by increasing the PUFA in their diets; on the other hand,
reducing the PUFA in their diets will elicit the opposite behavior. For what it’s worth, perhaps nothing to you,
I’ve always had a low tolerance to heat – the slightest increase in temperature
would make me break out in a sweat, and make my nose stuffy and ears bright
red. But since reducing the fat and increasing
the sugar in my diet (effectively reducing the PUFA in my body), my tolerance
to heat has improved and I layer up more than I used to as the ambient temperature
goes down.
Of course, there is a ceiling on the degree to
which the metabolic rate can be increased, being limited by the risk of
overheating from running things so quickly, among other things. But the main factor that limits a person’s
metabolic rate is the availability of oxygen.
Oxygen decreases the reliance on non-oxidative
metabolism, and, merely by the law of mass action, leads to more energy
generation and less fat storage. I
suppose exercise, by strengthening the heart and respiratory system – and
therefore blood circulation and lung ventilation – would help to increase the
efficiency of the delivery of oxygen to tissues. However, exercise need not be heavy and
exhaustive to be effective, only regular and consistent. Isotonic movements, in which tension is
applied and work is accomplished, is probably less stressful than isometric
movements, in which no work is performed but much heat is generated.[‡] The great force and resistance involved in
isometric movements tends to compress blood vessels to where blood perfusion
becomes greatly reduced so as to create a significant degree of tissue hypoxia,
resulting in a greater reliance on non-oxidative metabolism and higher levels
of lactate. Bulging muscles may look good
(I guess?) but they appear to come at a price.
But other stressors can decrease the availability
of oxygen to tissues, in part by increasing the use of fat for fuel. More glucose is used non-oxidatively as a
result, which, in turn, depletes glycogen and increases lactate and
acidity. As it happens, this
stress-induced oxygen depletion is usually offset because the increase in
acidity and lactate increases the efficiency with which oxygen moves from the
blood to tissues by way of the Bohr effect and the increase in 2,3-diphosphoglycerate
(2,3-DPG) within red blood cells. The
ratio of pyruvate to lactate is one of the best indicators as to the extent of oxidative
versus non-oxidative metabolism.
A healthy and robust metabolism implies low levels
of the stress hormones. Limiting the
stress hormones limits the use of fat for fuel and the production of lactate
and ensures the efficient turnover of ATP.
As it happens, ATP, bearing a high density of negative charge, binds and
keeps noradrenalin, positively charged under physiological conditions, inside
storage ‘bubbles’ inside cells, regulating their release.[§] (The
fact that both ATP and noradrenalin are involved in pain transmission further serves
to explain their co-localization inside cells.) The carbon dioxide and heat
generated as by products of metabolism both increase the delivery of oxygen to
tissues, like lactate does, and, stated above, more oxygen means more energy
generation and less fat storage. The
oxidative metabolism of glucose generates the most heat, carbon dioxide, and
ATP.
The capacity to use the increased oxygen is limited
by the availability of all the B vitamins, including thiamin, riboflavin, niacin,
pantothenic acid, and others. A regular
and adequate supply of these vitamins improves the reserve and capacity of the
Krebs cycle and respiratory chain. The
active thyroid hormone, T3, stimulates all the reactions involved in
the oxidative metabolism of glucose, increasing the requirement for all the B
vitamins. The ingestion of simple
carbohydrate also increases the requirement for the B vitamins, in particular
thiamin.3
If the body temperature cannot be kept up
naturally, the next best option is to keep warm artificially as to keep all the
chemical processes in the body operating as fast as they would at higher
temperatures. Trapped air is
particularly important to conserve heat in cold ambient temperatures. Therefore insulation, which for us means
clothing, is an important factor determining the amount of heat lost from the
body. The thickness, in particular, as
well as the looseness and color of the clothing determines how effective it is
as an insulator.
Questions I get a lot relate to digestion and the
simplest thing to do with problems concerned with digestion is to increase the
body temperature as high as to what’s tolerable. Not only is digestion, and therefore the
extraction of nutrients, slower at lower temperatures, but parasites and
bacteria also have a greater chance of breaking through the gut lining to cause
serious infections at those temperatures.
To make matters worse, the activity of the immune system decreases as the
temperature decreases, so the likelihood of mounting an effective immune
response to the pathogens that do get into the body decreases, too.[**] Within narrow limits, the temperature at
which the body ‘sets’ is determined by the composition of the fats in a person’s
diet: the most protective fats are the ones that are the most saturated.
The percentage of PUFA in tissues limits the rate
of energy expenditure. One reason for
this is that at higher temperatures, the spontaneous oxidation of PUFA –
therefore the production toxins – increases as the temperature increases. Since reading about hibernation as it relates
to PUFA in HLAF, I’ve been thinking
more and more about this idea. Lo and
behold, squirrels, professional hibernators, must carefully eat just the right
amount and kinds of nuts and seeds in order to store enough PUFA in their
tissues for a successful hibernation through the winter, but not so much as to
disrupt hibernation from the excessive production of toxic PUFA oxidation
products.
Although obesity in humans is associated with a
shorter lifespan, in wild animals there is no such association, unless they are
domesticated and deliberately fattened by humans. Obviously a multifactorial and complex
matter, the saturation index and therefore the fat composition of the diet, is
one factor that may explain these associations.4
 |
| log (maximum lifespan years) |
Combined with the observation that a higher
(resting) energy expenditure is generally associated with a longer lifespan5,6 we are beginning to move even further away from
the idea that fat is merely an inert sink in to which surplus nutrients are converted
and stored until they are needed elsewhere in the body.
The formation of fat from carbohydrate is an
extremely inefficient process – only by eating carbohydrate in incredible
amounts over long periods of time will a person begin to create and accumulate
fat made from carbohydrate.7 The conversion of carbohydrate to fat is simply a
highly energy-consuming process and the activity of the fat synthesizing
enzymes is not nearly as active as they are in other animals, like birds and
rodents. So the most efficient way to
change the fat composition of the body is by adjusting the fat composition of the
diet. Butter, cocoa butter, tallow, and
suet are among some of the most saturated and stable fats currently known. Good quality chocolate is unusually high in the
commonest saturated fats in mammals: palmitate and stearate. Shifting the diet to include more of these
fats and less of more unsaturated fats is sufficient to bring about the positive
changes discussed up to now.
Regarding lab tests to assess the state of
a person’s metabolism, unless the person is experienced interpreting those
tests, tests aren’t as important or informative as signs and symptoms are.
For instance, and because I received this
question recently, blood levels of histamine are useless because, as it
happens, histamine is concentrated locally.
So regardless of normal, or even low, levels of histamine in the blood,
a person could still be exposed to high amounts of histamine (and would benefit
from an anti-histaminic agent – my personal favorites being meclizine and diphenhydramine.)
Furthermore, having normal blood glucose
levels, as deemed by the “establishment,” does not as a matter of course imply
that there is a normal use of glucose by cells.
So despite normal blood glucose levels, it would be impossible to rule
out the existence of a deficit in energy production resulting from the
inadequate oxidative metabolism of glucose.
By the same token, high blood glucose levels do not necessarily spell
gloom and doom; in fact, it could mean quite the opposite. If cells are burning glucose intensely, for
instance, certain hormones are released that in turn stimulate the liver to
make more glucose in order to keep up with the increased demands for
glucose. A case in point is exercise,
during which glucose levels increase at the same time muscles are vigorously
burning glucose.
In cases such as these, a doctor may have
no choice but to declare a clean bill of health when the patient feels anything
but. Or, even worse, they may result in
treatments that are 180 degrees off the mark.
I’ve read too many cases like the one in which a person was declared to
have diabetes and was treated with drugs that, in one way or another, decrease blood
glucose levels despite the fact that the person’s symptoms did not line up with
that diagnosis all along.
I say all this to say that blood tests are not
foolproof in that when interpreting them, it should be remembered that
biological markers are dynamic in nature, and one test result merely represent
a snapshot in time. In many cases, a
proper diagnosis isn’t possible in the absence of multiple tests under
different conditions, such as when the patient is sick versus well. Given the complexity of diseases and the
variability among people, arriving at an accurate diagnosis is an art as much
as it is a science, guided by intuition as much as by years of experience and
practice. Sometimes, the response to an
empirical treatment is used to make a diagnosis.
Of all the signs and symptoms, monitoring the
axillary body temperature every morning will yield the biggest bang for your
buck. The temperature to aim for is about 98° F. The body temperature, in conjunction with
improvements in other non-specific signs and symptoms (e.g. fatigue, apathy,
drowsiness, mental depression) and general well-being should be used to guide treatment
decisions. Exercise, including isotonic contractions, improves cardiopulmonary fitness, and therefore the
delivery of oxygen, and increases musculature and bone density – both of which
increase the resting metabolic rate and the capacity for heat regulation. Small meals consisting of sugar and protein throughout
the day helps to keep the blood sugar up and the stress hormones down. Since the conversion of carbohydrate to fat
is so inefficient, adding small amounts of fat in the diet – in particular good
quality chocolate, butter, tallow, and suet – is protective.
REFERENCES
1. Hernández, A.
& Obregón, M. J. Triiodothyronine amplifies the adrenergic stimulation of
uncoupling protein expression in rat brown adipocytes. Am. J. Physiol.
Endocrinol. Metab. 278, E769–77 (2000).
2. Brand, M. D. Uncoupling to survive? The
role of mitochondrial inefficiency in ageing. Exp. Gerontol. 35,
811–20 (2000).
3. Lonsdale, D. A review of the
biochemistry, metabolism and clinical benefits of thiamin(e) and its
derivatives. Evid. Based. Complement. Alternat. Med. 3, 49–59
(2006).
4. Pamplona, R. et al. Mitochondrial
membrane peroxidizability index is inversely related to maximum life span in
mammals. J. Lipid Res. 39, 1989–94 (1998).
5. Speakman, J. R. et al. Uncoupled
and surviving: individual mice with high metabolism have greater mitochondrial
uncoupling and live longer. Aging Cell 3, 87–95 (2004).
6. Speakman, J. R., Selman, C., McLaren, J.
S. & Harper, E. J. Living fast, dying when? The link between aging and
energetics. J. Nutr. 132, 1583S–97S (2002).
7. Acheson, K. J. et al. Glycogen
storage capacity and de novo lipogenesis during massive carbohydrate
overfeeding in man. Am. J. Clin. Nutr. 48, 240–7 (1988).
[*] The metabolism required to maintain life.
[†] Because glycerol is not
taken back up into fat cells as efficiently as glucose is, for every round of
this substrate cycle, glucose is taken up from the blood and converted to
glycerol in fat cells.
[‡] Imagine straining at
stool while on the toilet as an example of an isometric movement.
[§] Noradrenalin bears a
positive charge under physiological conditions because the acidity (pKa) of its
amine groups is less than the acidity inside cells. So, more noradrenalin’s amine groups are
protonated, and therefore positively charged, under physiological conditions,
allowing them to form salt linkages with negatively charged ATP molecules.
[**] Fats also alter the
immune system directly. For instance, omega-3 fatty acids suppress
the immune system, decreasing the resistance to infections and wound healing; on the other hand, saturated fats do not suppress the immune system in the same way.
