Postmenopausal African American and Caucasian women performed aerobic exercise 3 or 4 times per week for 6 months. While both groups had similar positive results, the African American women experienced a greater reduction in resting metabolic rate.
The sample size was particularly small. Only 47 women participated and with control groups that puts each group at 11 or 12 each….small enough that one or two individuals might have skewed the results.
Compared to lean women, obese women have impaired leptin signaling leading to reduced insulin sensitivity. The defective signaling appears to be related to leptin receptors in subcutaneous fat but not visceral fat.
Leptin signals body fat levels to the brain, affecting appetite. High leptin levels are usually found in obese people (due to high body fat levels) but the message may not get through to the brain (because of impaired leptin signaling).
After high fat meals, women preferentially store fat in their legs. Storage in upper body subcutaneous tissue was similar in both sexes…suggesting that the men were preferentially storing the fat as visceral fat.
The researchers concluded that this was driven by increased LPL (lipoprotein lipase) activity in women, which is most likely mediated by estrogen. HL (hepatic lipase) increases visceral fat. High HL/LPL ratios lead to increased visceral fat in both sexes.
PMID: 16803856
The researchers used the drug bromocriptine (a D2R agonist) to simulate higher dopamine levels. Insulin sensitivity and fat oxidation improved.
Body weight did not improve during the time of the study, but improved insulin sensitivity and fat oxidation rates should improve body composition over time (the study only lasted 8 days). Resting energy expenditure was also increased by about 50 calories a day.
Dopamine is a neurotransmitter associated with ambition and reward. Higher dopamine levels also reduce appetite.