| BACKGROUND: Ghrelin is a potent GH secretagogue that also plays an
important role in appetite and weight regulation. Ghrelin increases
hunger and food intake, and its levels decrease after a standard meal
or glucose. OBJECTIVE: To examine the effects of standard oral glucose,
lipid and protein loads on ghrelin levels, investigating the possibility
that these responses may be modulated by several anthropometric and
metabolic factors. SUBJECTS AND METHODS: There were 24 adult nondiabetic
subjects (13 men/11 women; mean age 55.3 +/- 2.9 years, range 26-74
years). Each participant underwent one or more of the following nutrient
loads: (i) a standard oral glucose (75 g) load (n = 18); (ii) an oral
lipid load (40 g, with 24 g saturated fat; n = 13); (iii) an oral protein
load (40 g; n = 11). RESULTS: Fasting ghrelin levels were negatively
related to body mass index (BMI; r =-0.47; P = 0.02), waist circumference
(r = -0.58; P = 0.0028), waist/hip ratio (r = -0.56; P = 0.0046), fasting
insulin (r = -0.44, P = 0.03), and homeostasis model assessment insulin
resistance index (HOMA-R; r = -0.43, P = 0.034). Glucose load induced
a decrease in ghrelin levels (P < 0.0001), and this response was
modulated by sex (P < 0.0001), in that levels were significantly
higher in females. The presence of obesity affected ghrelin response
to glucose (< 0.0217), in that log-transformed ghrelin levels started
to increase back to baseline after its initial decline earlier in obese
than in lean subjects. Ghrelin levels after a glucose load were lower
over time in subjects with more pronounced insulin resistance (P < 0.0001).
Similarly, ghrelin levels decreased significantly following the lipid
meal (P = 0.035), and were modulated by HOMA-R (P = 0.027) and gender
(P = 0.029). Protein did not affect ghrelin levels. CONCLUSIONS: This
study demonstrates that ghrelin levels respond in a different manner
to glucose, lipid and protein loads, and are subject to modulation
according to gender, obesity and insulin sensitivity |
