Leptin is small protein that’s gotten a lot of press in the past few years. Because it’s able to act like a hormone, and is connected with fat metabolism, leptin has become a molecule of interest to many researchers – including drug companies – who see leptin as a possible tool in weight management. Results in the drug development area have not been very promising so far. However, during this period of time, we’ve learned some interesting facts about leptin, diet, and health.
First, exceeding low or high levels of leptin in our bloodstream appear to reflect health problems. High levels are associated with obesity, and also with higher percentages of body fat. High levels may also signify a change in the body’s sensitivity to leptin, where the body may have lost some of its responsiveness to this protein. Low levels appear to be associated with increased appetite, and difficulty reaching puberty during development. Most of the research in the above areas has been conducted on animals.
If possible, we would probably want to avoid both of the extremes described above. In terms of diet, one approach to avoiding these extremes may involve the level of fish we include in our meal plan.
Thanks to a study conducted on two African tribes and published in the July 2002 issue of Circulation: Journal of the American Heart Association, we may have gotten one clue about avoiding extremes in our blood leptin levels. In this study, higher levels of leptin, potentially associated with problems regulating fat metabolism, were found in low-fish diets. Fish-rich diets were associated with lower leptin levels and potentially fewer problems in regulating fat metabolism.
Here are a few quick serving ideas from the World’s Healthiest Foods to help you balance your leptin levels by enjoying fish more often:
- Combine cod, broth, healthy sautéed onions and garlic, and your favorite vegetables and seasonings in a stock pot to make a delicious fish soup.
- Make fish tacos by wrapping halibut, salsa and guacamole in a corn tortilla.
- Marinate snapper in citrus juice and honey, then bake.
For some exceptional recipes featuring these fish, click on the Recipe Assistant, select a fish from the healthy foods list, and click on the Submit button. A list containing links to all the World’s Healthiest Foods’ recipes containing the fish chosen will appear immediately below.
The researchers compared leptin levels in two closely related African tribal populations living in Tanzania. The two groups are essentially the same tribe, but they’re separated geographically. One group lives close to a lake, while the other lives inland. The inland-dwelling tribe eats a diet high in fruits and vegetables, while for the tribe living by the lake, freshwater fish is a main component of the diet.
The researchers studied 279 people on the high fish diet and 329 who ate the vegetarian diet. They compared average daily calorie intake and food consumption, BMI (body mass index, a measure of body fat based on height and weight), body fat content, age and gender. Skin-fold thickness was also used to assess body fat. Leptin, insulin and glucose levels were measured after an overnight fast.
The average BMI among the people in the study, regardless of diet, was 20. A BMI value from 18.5 to 24.9 is considered healthy; BMI from 25.0 to 29.9 is overweight; and a BMI value of 30 or greater is obese.
Average daily calorie intake was similar for both groups—2196 for the fish-rich diet and 2109 for the vegetarian diet. The fish-rich diet consisted of 300-600 grams (or approximately 10-20 ounces) of fish per day, with 60-120 grams (g) of maize (corn), 40-60g of beans, 20-40g of spinach, 40-60g of potatoes and 30-50g of rice. The vegetarian diet included negligible amounts of fish with 150-350g of maize, 70-140g of beans, 60-100g of spinach, 100-200g of potatoes and 80-120g of rice.
Among those on the fish diet, men had average leptin levels of 2.5 nanograms per milliliter (ng/mL), and women had an average of 5.0 ng/mL. In comparison, among the tribe eating primarily vegetables, men had average leptin levels of 11.2 ng/mL, and women had average levels of 11.8 ng/mL.
Leptin, which is secreted by fat tissue, may act as a satiety messenger, which in normal-weight people signals “stop eating,” when they have consumed enough food. As people gain weight, however, the body may stop listening to leptin’s message, so more leptin may be produced to get the message across, explains senior author Virend K. Somers, M.D., D. Phil., professor of medicine in the division of cardiovascular disease and hypertension at the Mayo Clinic, Rochester, Minn.
Among the African populations in this study, however, higher body fat was not clearly associated with increased leptin levels. “Regardless of body fat or body mass index (BMI), leptin levels were substantially lower among the fish-eaters than among vegetarians,” says Somers. “We speculate that a fish diet may change the relationship between leptin and body fat and somehow help make the body more sensitive to the leptin message.”
Leptin’s effects on health are not limited simply its relation role in satiety and fat metabolism, but higher levels also correlate with insulin resistance and other markers of the metabolic syndrome, popularly dubbed “Syndrome X,” in which the body’s ability to effectively utilize glucose lessens. Syndrome X is thought to be an initial warning sign of increasing risk for type 2 diabetes.
An earlier study of more than 1,000 men in Scotland published in Circulation in 2001 found that high leptin levels could be used to identify men at increased risk for a heart attack. For each standard deviation increase in leptin levels, the men’s relative risk for heart attack increased by 125%.
In this study, leptin levels were found to correlate with levels of C-reactive protein, a marker of inflammation that is a coronary heart disease risk factor considered even more significant than cholesterol levels. The higher the men’s leptin levels, the higher their C-reactive protein.
In the African tribe study, lead researcher Somers says the low leptin levels among the fish-eating women were particularly noteworthy. Women usually have higher leptin levels than men, but in this study, women who ate the fish-rich diet had lower leptin levels than either the women or the men on the vegetarian diet.
Somers says this finding fits with earlier studies that showed diets high in fish were associated with an improved cardiovascular risk profile, and adds “These results add to the increasing body of evidence pointing to the benefits of fish consumption.”
Fish consumption is very low in most American’s diets, although The American Heart Association recommends at least two servings of fish a week.
References: Somers V, Winnicki M, Phillips B, Accurso V, Puato M, Palatini P, Pauletto P. Fish-rich tribal diet linked with low leptin levels. July 2, 2002 Rapid Access Issue, Circulation. Wallace AM, McMahon AD, Packard CJ, Kelly A, Shepherd J, Gaw A, Sattar N. Plasma leptin and the risk of cardiovascular disease in the west of Scotland coronary prevention study (WOSCOPS). Circulation 2001 Dec 18;104(25):3052-6.