Lower insulin sensitivity found In Mexican-Americans, regardless of behavioral and metabolic factors

November 05, 2002

(October 31, 2002) - Bethesda, MD - The population of Mexican-born individuals in the United States is 8.5 million. Nearly 60 percent of American Latinos are of Mexican origin, and the number of people living in the US who are of Mexican origin is more than 20 million. The population explosion of this group in America is "old news."

Perhaps the most significant -- and least known -- consequence of the growth of this demographic group is to the nation's health care system. Not because of the current issues surrounding the delivery of primary care services - but for the future services that will be necessary to diagnose and treat a population highly susceptible to type 2 diabetes.

Background Mexican-Americans are diagnosed with type 2 diabetes mellitus (T2DM) two to three times more frequently than are non-Hispanic white (NHW) Americans. Scientists have found that insulin resistance is key in the cause for the disease; studies have revealed that Mexican-Americans of both genders and all ages demonstrate greater levels of insulin resistance when compared to the NHW population.

Although the reasons are unclear, some suggest that genetic factors could explain the higher prevalence of insulin resistance in this Hispanic population group, considering that 35 percent of their genetic Mexican-American make-up is attributable to Native American ancestry.

It is also possible that lifestyle factors, including diet and exercise, contribute to the ethnic differences in insulin resistance. Visceral adiposity (obesity), exercise, and dietary fat have all been shown to impact peripheral insulin resistance.

The Study A new research study that compares behavioral, metabolic, and molecular behavior between Mexican-Americans and non-Hispanic whites offers new clues on why public health officials need to act on this potential problem now. At the same time, the current study findings can provide an important first step to this problem that could easily be undertaken by school systems, restaurants, and all institutions that meet the dietary needs of our citizens and residents from the south.

The authors of "Behavioral, Metabolic, and Molecular Correlates of Lower Insulin Sensitivity In Mexican-Americans," are Richard C. Ho, Kevin P. Davy, Matthew S. Hickey, Scott A. Summers, and Christopher L. Melby, all from Colorado State University, Fort Collins, Colorado. Their findings appear in the October 2002 edition of the American Journal of Physiology--Endocrinology and Metabolism, a journal of the American Physiological Society (APS).

[In previous studies, Mexican-Americans have been shown to exhibit lower insulin sensitivity independently of body fat and body fat patterning. However, this issue is not entirely resolved given that studies that have documented diminished insulin sensitivity in non-obese, non-diabetic Mexican-Americans compared with NHW utilized less sensitive methods to estimated Mexican-American body fat and central adiposity (obesity). Furthermore, the possible contribution of lower physical activity and physical fitness in this demographic group as well as differences in dietary intake were not accounted for in these studies. Because Mexican-Americans compared with NHW tend to exhibit greater central adiposity, are less physically active, and consume a more atherogenic diet, it is important to examine these factors as possible contributors to the lower insulin sensitivity in Mexican-Americans.]

This study had two specific aims: First, to determine whether or not differences in insulin sensitivity persist between these two groups after controlling for the effects of acute and chronic exercise, abdominal fat distribution, and dietary intake. Second, to ascertain whether Mexican-Americans exhibit lower skeletal muscle protein concentrations of IR , PI3K p85, Akt1, Akt2, and GLUT4 compared with NHW after controlling for these same potential confounders.

Methodology: Thirteen (13) non-obese Mexican-Americans (seven females, six males) were matched to 13 non-obese NHW (seven females, six males) age 18-40, on the basis of gender, age, and aerobic fitness.

Subjects were eligible for participation on the basis of the following characteristics: being nonsmoking, apparently healthy individuals with no overt signs or symptoms of disease as determined by a medical history, and having normal fasting blood glucose, no past or present history of endocrine disorders, and resting blood pressure of 110/90 mHg. To be appropriately identified as Mexican-Americans, each participant traced his/her ethnicity to all four grandparents. The Colorado State University Human Research Committee approved the study protocol.

The researchers looked at a number of variables, including body mass, height, and composition. Results

The researchers found that: Conclusions

There are three major significant findings in this study: This study demonstrates that lower insulin sensitivity persists in non-obese, non-diabetic Mexican-Americans compared with their non-Hispanic white counterparts, even after acute and chronic effects of exercise and abdominal fat distribution are accounted for. Furthermore, protein abundance of skeletal muscle IR , PI3K p85, Akt1, Akt2, or GLUT4 does not explain these differences. Differences in insulin sensitivity are lost when dietary intakes of palmitate and palmitoleate are accounted for, suggesting the possibility that these factors may contribute to the lower insulin sensitivity seen in Mexican-Americans.
Source: October 2002 edition of the American Journal of Physiology--Endocrinology and Metabolism.

The American Physiological Society (APS) was founded in 1887 to foster basic and applied science, much of it relating to human health. The Bethesda, MD-based Society has more than 10,000 members and publishes 3,800 articles in its 14 peer-reviewed journals every year.

American Physiological Society

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