Diet rich in fish associated with lower plasma leptin, independent of body fat

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There are several novel findings evident from the present study.

Compared with their vegetable diet counterparts, both men and women on

a fish diet had markedly lower leptin levels, despite having almost

identical BMIs. Although prior studies have consistently reported

higher leptin levels in women than in men,12 women on the fish diet

had leptin levels less than half those observed in men on a vegetarian

diet. The fish-eating men and women had leptin levels even lower than

the values observed in persons heterozygous for a frameshift mutation

in the ob gene.3 In contrast to other studies,4,12 the present study

was unable to demonstrate any independent relationship between plasma

leptin and body fat composition, except for a very weak positive

association in fish-eating women. Overall, these data suggest that a

fish diet is accompanied by lower leptin and may alter the usual

feedback relationships between leptin levels and body fat and that

plasma leptin levels do not always reflect BMI or the amount of body fat.

Our findings may have relevance in understanding the relationship

between a predominantly fish diet and cardiovascular disease. Higher

leptin concentrations have been prospectively implicated as an

independent risk factor for stroke, coronary artery disease, and

myocardial infarction.5–7 Prospective studies have shown that a diet

rich in fish or fish oil is related to a low incidence of

cardiovascular disease.13 The mechanisms of the protective effect of

fish oil on cardiovascular risk have been attributed mainly to the

high concentration of n-3 polyunsaturated fatty acids and their

antithrombotic action and modification of immunological

processes.14,15 The fish diet that we have studied is also associated

with lower blood pressure and a favorable lipid profile.11 We

speculate that an additional potential benefit of a fish-rich diet on

cardiovascular risk may be the reduction in plasma leptin concentrations.

There are several limitations of the present study. First, only lean

black Africans were studied. Different relationships between fish

diets and leptin may exist in obese subjects and in different races.

Second, other unknown dietary or behavioral factors may contribute to

the apparent effect of the fish diet on leptin concentrations.

However, the food questionnaire used was validated by previous

nutrition analyses carried out in Tanzania.11 Third, underlying

genetic factors may contribute to the difference in plasma leptin

concentrations. However, both dietary groups belong to the same tribe,

speak the same dialect, live near each other, and have similar calorie

intakes, lifestyles, and BMI values. The only difference was the type

of diet.

In conclusion, we show that a diet rich in fish is associated with

lower plasma leptin concentrations, independent of body fat or BMI,

suggesting that this kind of diet may improve leptin sensitivity. In

subjects on a fish diet, leptin levels are even lower than those

documented in persons heterozygous for a frameshift mutation in the ob

gene.3 The low leptin in subjects on a fish diet is not necessarily

associated with increases in BMI or body fat. These findings may have

implications for understanding the reduced cardiovascular risk in

subjects on a fish-rich diet.

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Leptin:

http://arbl.cvmbs.colostate.edu/hbooks/pathphys/endocrine/bodyweight/leptin.html