A Salad and Cooking Oil
MCTs reduce food intake and increase energy output
By Aaron W. Jensen, Ph.D.
ave you ever wondered what makes you feel hungry
- why that
persistent growl in your stomach drives you to leave your comfortable place on
the sofa and ravage the fridge for tempting morsels? Scientists have long tried
to understand what drives our craving for food, and they have come up with a
simple answer: hormones.
Hormones are your body's messenger molecules: they're made
in one organ (sometimes a few) and travel elsewhere to prompt your body to
respond in some way. In the case of hunger, hormones made in the digestive
system travel all the way to the brain to make sure that you seek food to make
your stomach happy. Most of us know all too well just how effective those
hormones can be.
Compared with LCTs, MCTs have
a lower caloric content; they
typically don't get stored in
fat cells; and they stimulate
thermogenesis by raising the
body's basal metabolism rate.
Scientists are still working out the details of this complex
communication system between your gut and your head, but they have sketched in
some of the important players that let your body know whether it should track
down food or stay on the sofa. One of the most important hormones in triggering
hunger is called ghrelin. Made by the stomach when it is empty, ghrelin sends a
signal that says "I'm hungry" to the brain. Neurons in the hypothalamus (a part
of the brain that regulates appetite, as well as sexual desire and sleep)
respond by instructing the body to seek food (which usually means a quick trip
to the fridge or turning the car into the nearest drive-thru).
Putting the Brakes on Eating
Clearly, if you succumbed to the powers of ghrelin too
easily, serious weight gain would result. That's why it's good that you also
have hormones to put the brakes on your appetite and send the "I'm full" signal
to your brain. These satiety hormones are called PYY (peptide YY) and CCK
(cholecystokinin). PYY and CCK are produced toward the end of a meal and are
responsible for giving you that satisfied, full feeling (see the sidebar
"Hormones - The Key to Appetite Suppression"). Of course, we all know that these
signals can be overridden - just think, for example, of that bloated
"I-wish-I-hadn't-eaten-all-that-food" feeling you get following a Thanksgiving
feast.
MCTs Help Suppress Appetite
The "I'm full" signal is triggered more effectively by some
foods than others. In general, fats are the most effective dietary ingredients
for inducing the production of PYY and CCK, thus reducing the desire to eat.
Not all fats are equally effective in suppressing appetite, however. Medium-chain
triglycerides (MCTs), for example, appear to be more effective than the far
more common long-chain triglycerides (LCTs) when it comes to ratcheting down
those hunger pangs. The inclusion of MCTs in your diet - in the form of salad oil
or cooking oil - can thus offer yet another aid in your battle for weight
control.
MCTs are different from most dietary fats. Compared with
LCTs, which likely account for most or all of your current fat intake, MCTs
have a lower caloric content; they typically don't get stored in fat cells; and
they stimulate thermogenesis (energy output in the form of heat) by raising the
body's basal metabolism rate, which is a measure of the amount of energy
expended in performing basic involuntary functions, such as breathing, digestion,
and heartbeat.
MCTs Increase Satiety
MCTs work by several different mechanisms to help you rein
in your weight. One has to do with satiety, the feeling of satisfaction brought
on by a full stomach. Researchers in France fed different groups of people breakfasts
that were either low in fat or rich in one of several types of fat: MCTs,
saturated LCTs (e.g., lard), and unsaturated LCTs (e.g., olive oil); they then
observed behavioral and metabolic responses to these different meals.
During the study, all the subjects were restricted to rooms
that contained no time cues: they were kept under artificial light, with no
windows and no time-keeping devices, and they were allowed to request food when
they were hungry again. The length of time before the next meal requests (lunch
and dinner) was monitored, as was the amount of food (caloric content) consumed
at each of those meals.
The researchers found that the low-fat breakfasts resulted
in significantly shorter time intervals between meal requests than did the fat-rich
breakfasts. This is not surprising, considering that fats are best at
triggering the satiety response. It follows that diets with the most fat would
induce the greatest satiety and allow the subjects to remain food-free for the
longest intervals.
Over the 7-day period, women on
the MCT diet burned over 350
more
Calories than those on the LCT diet.
MCTs Result in Less Food Intake
With respect to breakfasts rich in either MCTs or LCTs,
there was no difference in the time intervals between breakfast and lunch.
However, the amount of food consumed by the MCT group at lunch was
significantly less than the amounts consumed by either the LCT group or the
low-fat group. The total caloric content of the lunch consumed by the MCT group
was 18.4% lower than that of the saturated-LCT group, 16.5% lower than that of
the low-fat group, and 5.4% lower than that of the unsaturated-LCT group. The
authors concluded that MCTs modified food intake in these subjects via a
"postabsorptive mechanism" that enhanced satiation and decreased food
consumption at the next meal.
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Hormones - The Key to Appetite Suppression
Scientists have known about the function of the hormone CCK
for a long time. The small intestine starts secreting this molecule at the end
of a meal and primes the digestive system to start breaking down fats (the last
portion of a meal to enter the intestine from the stomach). For example, CCK
stimulates the gallbladder to contract and release bile into the small
intestine to help digest fats. But that's not all it does - it also enters the
bloodstream and is transported to the brain, where it acts to suppress
appetite. In fact, the common problem of reduced appetite in the elderly is
believed to be caused in part by elevated levels of CCK.
The hormone PYY has received much more press recently,
thanks in large part to an article that appeared in the British journal
Nature. This research demonstrated that injecting PYY into the bloodstream of
healthy volunteers reduced their food intake by one-third over a 24-hour
period. PYY is normally produced in the gastrointestinal tract following a
meal, and the amount produced appears to correlate closely with total caloric
intake. So the more you eat, the more PYY you produce, and the less food you
eat at the next meal. PYY sounds like a great candidate for a supplemental
appetite suppressant, but it is likely to be at least another decade before our
knowledge of it can be turned into a useful weight-control therapy.
References
- MacIntosh
CG, Morley JE, et al. Effect of exogenous cholecystokinin (CCK)-8 on food
intake and plasma CCK, leptin, and insulin concentrations in older and young
adults: evidence for increased CCK activity as a cause of the anorexia of
aging. J Clin Endocrinol Metab 2001;86:5830-7.
- Batterham RL, Dowley MA, Small CJ, et al. Gut
hormone PYY(3-36) physiologically inhibits food intake. Nature 2002;418:650-4.
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MCTs - A Better Kind of Fat
All fats are not created equal. We know that unsaturated
fats (both monounsaturated and polyunsaturated forms) have substantial health
benefits compared to saturated fats (think of the Mediterranean diet rich in
monounsaturated olive oil). And of these, the omega-3 fatty acids (fatty acids
are precursors to fats) found in coldwater fish oils are especially beneficial
with respect to mental function and cardiovascular health.
All fats consist of a molecule of glycerol to which up to
three hydrocarbon chains are attached (when it's three, the molecule is a
triglyceride, the most common form of fat). These chains, of varying length,
are derived from fatty acids, which are found naturally in our foods. Our
bodies process different kinds of fats differently, depending in part on the
length of the hydrocarbon chains as well as on their degree of saturation with
hydrogen atoms. Most dietary fats, such as those mentioned above, are
long-chain triglycerides (LCTs), with hydrocarbon chains typically containing
14 to 22 carbon atoms.
Medium-chain triglycerides (MCTs) are smaller, with chains
of 6 to 12 carbon atoms, but with a strong preponderance of 8-carbon and
10-carbon chains. MCTs are easier for the body to deal with - they can be
absorbed directly from the gut and sent to the liver for rapid processing. By
contrast, LCTs must be subjected to digestive enzymes in the gut, converted to
a new form in the intestinal cells, and incorporated into molecular transport
vehicles for delivery to the liver for processing. This helps explain why MCTs
are a good fat source for people with malabsorption syndrome, in which ordinary
dietary fats are poorly absorbed by the body owing to various dysfunctions of
the pancreas, liver, digestive system, or lymphatic system.
Another important difference between MCTs and LCTs is that
MCTs are less energy-rich than their long-chain cousins. This means that if you
consumed the same weights of MCTs and LCTs, you would be getting fewer Calories
from the former: 8.2 Calories per gram of fat from MCTs, versus 9.0 from LCTs
(a 9% reduction). Over time, a difference like that will really make a
difference.
- Ingle KL, Dreidger A, Traul KA, Nakhasi DK.
Dietary energy value of medium-chain triglycerides. J Food Sci 1999;64:960-3.
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In terms of weight control, these are exciting results,
suggesting that MCTs may play a significant role in suppressing appetite. It is
important to keep these results in perspective, however, and remember that they
derive from a study that focused on a single day's food intake. Further
research is needed to determine whether sustained dietary intake of MCTs has a
long-term impact on appetite, as well as to shed more light on how specific
hormones are involved in this appetite-suppression response.
MCTs Increase Energy Expenditure
Longer studies with MCTs have also been performed, but with
different objectives in mind. Canadian researchers focused on energy
expenditure in individuals maintained on either MCT- or LCT-enriched diets;
they investigated the impact that MCTs had on 12 nonobese premenopausal women over
a 2-week period. For 14 straight days, all the women were fed the same types
of food, but one group's meals were prepared with LCTs, while the other group's
meals were prepared with MCTs. That was the only difference, and the total
amount of food served was the same for both groups.
On days 7 and 14 of the trial, the researchers recorded the
women's total energy expenditure and basal metabolism rate. On day 7, both
measures were significantly higher in the MCT group: the basal metabolism rate
had increased by 4.4%, and the total energy expenditure had increased by 3.1%.
To put this in perspective, the amount of energy expended
increased by 52 and 45 Calories per day, respectively.* Over the 7-day period,
women on the MCT diet burned over 350 more Calories than those on the LCT diet.
This increased caloric output was due solely to differences in the dietary fat,
not to any other factor, such as increased exercise. On day 14 of the study,
the total energy expenditure in the MCT group continued to be higher than that
in the LCT group, but the increase was not as dramatic as that observed on day 7.
MCTs - A Recipe for Success
In a marketplace that touts miracle diets, overnight weight
loss, and "ripped abs" without the bother of exercise, the above results may seem
unremarkable. But when you add up all the individual benefits of MCTs, it
becomes clear that including this type of fat in your diet may offer
significant benefits. Consider, for example, that MCTs have a lower caloric
content than LCTs on a per weight basis (see the sidebar "MCTs - A Better Kind of
Fat"); they can reduce overall food intake in the short term; and they increase
the rate at which your body burns Calories. That sounds like a recipe for
success that we can all benefit from in the age-old battle against an
increasing waistline.
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MCT oil can be incorporated into your diet in a convenient
manner: in salad dressing, e.g., for sautéing (but not frying - the temperatures
are too high), or to add a little flavor to steamed vegetables.
MCTs should be used, however, as a supplemental oil, not as
a replacement oil. We recommend a serving size of 1-3 tablespoons per day.
Larger amounts of MCT oil may result in stomach discomfort or diarrhea.
Servings of over 5 tablespoons taken at one time can result in intense
intestinal cramping. Start with 1 teaspoon of MCT oil and slowly increase the
amount over several days to your desired dietary level.
Diabetics and those with liver disorders should approach the
use of MCTs with caution, as the fat tends to be burned rapidly in the liver.
Individuals with these conditions should avoid MCTs entirely or use them only
under a doctor's supervision.
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References
- St-Onge M-P,
Jones PJH. Physiological effects of medium-chain triglycerides: potential
agents in the prevention of obesity. J Nutr 2002;132:329-32.
- Van
Wymelbeke V, Himaya A, Louis-Sylvestre J, Fantino M. Influence of medium-chain
and long-chain triacylglycerols on the control of food intake in men. Am J Clin
Nutr 1998;68:226-34.
White MD, Papamandjaris AA, Jones PJH. Enhanced
postprandial energy expenditure with medium-chain fatty acid feeding is
attenuated after 14 d in premenopausal women. Am J Clin Nutr 1999;69:883-9.