Eight weeks of overfeeding alters substrate partitioning without affecting metabolic flexibility in men

Background/Objective

Impairments in metabolic flexibility and substrate handling are associated with metabolic syndrome. However, it is unknown whether metabolic inflexibility causes insulin resistance. We therefore measured metabolic flexibility and substrate handling before and after 8 weeks of overfeeding in initially healthy adults, as a model of the early stages of insulin resistance.

Subjects/Methods

Twenty-nine healthy men (27 ± 5 years old; BMI 25.5 ± 2.3 kg/m²) were overfed by 40% above baseline energy requirements for 8 weeks and gained 7.6 ± 2.1 kg of weight. Before and after overfeeding, energy expenditure, substrate oxidation, and metabolic flexibility were measured in 2 ways: a) during 1 day of eucaloric feeding in a whole-room indirect calorimeter, and b) during a two-step hyperinsulinemic-euglycemic clamp.

Results

Eight weeks of overfeeding decreased insulin sensitivity at low and high doses of insulin (p=0.001 and p=0.06, respectively). This was accompanied by decreases in the respiratory quotient (RQ) while sleeping (0.877 ± 0.020 to 0.864 ± 0.026; p=0.05) and at low insulin levels during the clamp (0.927 ± 0.047 to 0.907 ± 0.032; p=0.01). Overfeeding did not affect metabolic flexibility as measured during a clamp (p≥0.17), but it tended to increase 24-hour metabolic flexibility (awake – sleep RQ) as measured by chamber by 0.010 ± 0.028 (p=0.08). In terms of substrate oxidation, overfeeding increased protein oxidation (13 ± 23 g/day; p=0.003) and tended to increase fat oxidation (6 ± 16 g/day; p=0.07), but did not affect carbohydrate oxidation (p=0.64). Individuals with greater metabolic adaptation to overfeeding had higher carbohydrate oxidation rates (r=0.66, p=8×10⁻⁵) but not fat oxidation rates (p=0.09).

Conclusions

The early stages of insulin resistance are accompanied by modest declines in the RQs during sleep and during a clamp, with no changes in fasting RQ or signs of metabolic inflexibility. Our data therefore suggest that metabolic inflexibility does not cause insulin resistance.

Lifestyle modification intervention improves glycemic control in Mongolian adults who are overweight or obese with newly diagnosed type 2 diabetes

Objective

To evaluate the effectiveness of a weight loss intervention in Mongolian adults with newly diagnosed type 2 diabetes mellitus and with BMIs ≥ 25.0 kg/m².

Methods

Eighty participants (33 men/47 women) aged 32–56 years old received education sessions to improve nutritional habits and increase physical activity. Participants were counselled in‐person on two occasions with regular follow‐up by phone to eat less (reduce calorie intake by 30–40% and consume fewer fatty foods), shift food intake to earlier in a day and increase physical activity such as walking, jogging, running and biking. Measurements were performed before and after the 6‐month intervention.

Results

After 6 months, the average weight loss was 4.3 ± 4.7 kg, representing a 4.9 ± 5.4% reduction in body weight (p < 0.0001). Mean HbA1c decreased from 8.5 ± 2.7% to 6.0 ± 1.8% (p < 0.0001), and the percent of individuals with HbA1c in the diabetic range dropped from 76.3% to 27.5%. These changes were accompanied by marked improvements in cardiovascular risk factors, including total cholesterol (3.92 ± 1.02 to 3.13 ± 0.80 mmol/l; p < 0.0001) and triglycerides (2.11 ± 0.82 to 1.54 ± 0.51 mmol/l; p < 0.0001), and modest reductions in systolic and diastolic blood pressure (p < 0.05).

Conclusion

The remarkable improvement in glycemic control and lipid profile in participants suggests that a lifestyle modification intervention targeting weight loss may be highly effective for early diabetes treatment and prevention in Mongolians.

Eight weeks of dietary overfeeding increases renal filtration rates in humans: implications for the pathogenesis of diabetic hyperfiltration

OBJECTIVE

Diabetic nephropathy is characterized at its onset by glomerular hyperfiltration. Prospective studies in humans measuring filtration rates with weight gain are lacking. We investigated renal filtration following weight gain induced by overfeeding.

DESIGN

Eight weeks of overfeeding (40% above energy requirements, 44% fat, 15% protein and 41% carbohydrate) as well as a 6-month follow-up after the overfeeding intervention.

SUBJECTS

Thirty-five participants (age: 26.7 ±5.3 years; body mass index: 25.5 ± 2.2 kg m(-2) ; 29 m/6f).

MEASUREMENTS

Creatinine clearance rate (Ccr) from 24-h urine collection, estimated glomerular filtration rate (eGFR) from the modification of diet in renal disease (MDRD), insulin sensitivity/glucose disposal rate (GDR) by a euglycemic-hyperinsulinemic clamp, components from basic metabolic panels and serum lipid panels.

RESULTS

Both eGFR and Ccr increased with overfeeding (P = 0.04) and serum lipids (all P < 0.05), along with a decrease in insulin sensitivity (P = 0.003). Fasting glucose concentration was not affected (P = 0.98), but the per cent change in Ccr correlated positively with the change in GDR with overfeeding (r = 0.39, P = 0.02). Six months following overfeeding, serum glucose was maintained, and no evidence of urinary glucose was observed at any time-point.

CONCLUSIONS

These data suggest that renal hyperfiltration may act as a mechanism to preserve insulin sensitivity through maintenance of systemic glucose homoeostasis with caloric excess.