The Food That Helps You Lose Fat
Losing weight isn't as difficult as it sounds — it's trying
to keep it off for good that's the real challenge.
Eating is a powerful drive. If you've lost a lot of weight, you're
probably familiar with that intense sense of hunger, which just
won't go away. The usual advice to just "eat less" is
a lot easier for me to write than it is for you to do.
One of the hormones responsible for the increase in hunger is known
as leptin. Leptin (the Greek term for thin) is a hormone
released by your fat cells. When you lose fat, leptin levels drop.
When you gain fat, leptin levels rise.
Once leptin has been secreted by your fat cells, it travels to
the hypothalamus. This is the part of your brain that controls
eating behavior. Once it's there, leptin activates anorectic nerve
cells, which suppress your appetite. At the same time, leptin
prevents
orexigenic cells from stimulating your appetite.
Although it interacts with
a number of hormones and has other important functions, the role
of leptin in appetite control looks something like this; when
leptin levels drop, you get hungry. When they go up, you feel
full.
The good news is that you might be able to change the way your body responds to leptin...
simply by eating more fish!
Scientists have known for some time that fish oil affects leptin
levels in rats [3]. But Dr. Mikolaj Winnicki and his colleagues
from the Mayo Clinic wanted to see if a fish-rich diet has a similar
effect in humans [1].
The findings, published in the journal Circulation, come
from a comparison of two neighboring tribes near Lake Nyasa in Tanzania.
In the population of the village Lupingu, located near to a river,
fish provides almost 25% of the total daily calorie intake. The
villagers in Madilu, a nearby village located inland, eat very
little fish. Both tribes consume a similar number of calories
per day, and lead very similar lifestyles.
Average daily calorie intake was 2196 for the fish diet and 2109
for the no-fish diet. The fish diet consisted of 300-600 grams of
fish per day, with 60-120 grams of maize (corn), 40-60 grams of
beans, 20-40 grams of spinach, 40-60 grams of potatoes and 30-50
grams of rice.
The no-fish diet included negligible amounts of fish with 150-350
grams of maize, 70-140 grams of beans, 60-100 grams of spinach,
100-200 grams of potatoes and 80-120 grams of rice.
Leptin
Regardless of their body fat levels, the fish-eating tribe was
found to have much lower levels of leptin.
That's despite the fact that body fat — usually an important
indicator of leptin levels — was similar in both groups. Leptin
is made in fat cells; the more fat you have, as a rule, the more
leptin you make.
In the tribe eating fish, men had an average leptin level of 2.5
nanograms per milliliter, compared with 11.2 in the mainly vegetarian
tribe.
Although leptin levels are usually higher in women, the researchers
found the leptin levels of women who ate fish to be less than half
that of both the female and male vegetarians.
Although it might seem counterintuitive, many obese individuals
actually have high levels of leptin. On the face of it, this appears
to blow all of the theories regarding
leptin and weight loss out of the water.
After all, if obese people have high levels of leptin, surely they
shouldn't be obese in the first place.
While obese people do have high levels of leptin circulating in
their body, the leptin isn't active where it needs to be —
the hypothalamus. Instead, they seem to have developed a form of
leptin resistance, where leptin is unable to make the "jump"
from the blood to the brain [2].
This latest study suggests that a fish-rich diet somehow makes
your body more sensitive to leptin, and might play a small (but
important) role in helping you lose weight and keep it off for good.
As with all research, this study does have limitations.
First, only lean black Africans living in a rural environment were
studied. We don't know if the findings will apply to a semi-overweight,
urban-dwelling population. Fish-rich diets might affect leptin differently
in obese subjects and in different races.
What's more, this study only describes a link or association between
a fish-rich diet and lower leptin levels. It doesn't show that one
is causing the other. Remember that association does not
mean causation. And leptin is just one of many factors influencing
hunger and calorie intake.
According to the diet questionnaires, the Lupingu villagers were
eating 300-600 grams of fish per day. That's a lot of fish.
If you were to eat this amount of fish every day, you'd probably
end up getting a lot of mercury. Some forms of mercury — such
as methylmercury — are toxic to both humans and animals. Even
wild fish contain mercury, although the levels vary depending on
the type of fish.
Although fish oil supplements contain no mercury, tests show that
some of them contain organic pollutants such as dioxins and dioxin-like
polychlorinated biphenyls.
The bottom line
There are still many more questions than answers about fish oil
and leptin. And it would be hard to make a solid case for eating
more fish based on this study alone.
However, the long-chain omega-3 fatty acids in fish have been linked
with everything from a reduction in the risk of heart disease to
improved mental function.
If you're not eating oily fish with a relatively low mercury content
(such as salmon) several times a week, or using a high-quality
fish oil supplement, now would be a good time to start.
About the Author
 Christian Finn holds a master's degree in exercise science, is a certified personal trainer and has been featured on BBC TV and radio, as well as in Men's Health, Men's Fitness, Muscle & Fitness, Fit Pro, Zest and other popular fitness magazines.
If you want better, faster results from the time you spend in the gym, click here now for instant access to his step-by-step muscle-building and fat-burning workout routines.
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References
1. Winnicki, M., Somers, V.K., Accurso, V., Phillips, B.G., Puato,
M., Palatini, P., & Pauletto, P. (2002). Fish-rich diet,
leptin, and body mass. Circulation,
106, 289-291
2. Caro, J.F., Kolaczynski, J.W, Nyce, M.R., Ohannesian, J.P.,
Opentanova, I., Goldman, W.H,, Lynn, R.B., Zhang, P.L., Sinha,
M.K., & Considine,
R.V. (1996). Decreased cerebrospinal-fluid/serum leptin ratio in
obesity: a possible mechanism for leptin resistance. Lancet,
348, 159-161
3. Peyron-Caso. E., Taverna, M., Guerre-Millo, M., Veronese, A.,
Pacher, N., Slama, G., & Rizkalla, S.W. (2002). Dietary (n-3)
polyunsaturated fatty acids up-regulate plasma leptin in insulin-resistant
rats. Journal
of Nutrition, 132, 2235-2240
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