| Summary: | Abstract Objective We have been interested in determining the effects of dietary changes on fuel metabolism and regulation in men with type 2 diabetes mellitus (T2DM). In this study, the changes in 24‐hr circulating lipid profiles were determined when the major fuel source was endogenous versus exogenous fat. Methods Seven males with T2DM were randomized in a crossover design with a 4‐week washout period. A standard mixed (control) diet (30%fat:15%protein:55%carbohydrate) was provided initially. Subsequently, a 72‐hr (3‐day) fast, or a high fat (85%), 15% protein, essentially carbohydrate‐free (CHO‐free) diet was provided for 72 hr. Triacylglycerol (TAG), non‐esterified fatty acids (NEFA), β‐hydroxybutyrate (bHB), and insulin‐like growth factor‐binding protein‐1 (IGFBP‐1) profiles were determined during the last 24 hr of intervention, as well as during the control diet. Results Regardless of the amount of dietary fat (30% vs 85%) and differences in 24‐hr profiles, TAG, NEFA, and bHB all returned to the previous basal concentrations within 24 hr. TAGs and NEFAs changed only modestly with fasting; bHB was elevated and increasing. The IGFBP‐1 profile was essentially unchanged with either diet but increased with fasting. Conclusion A CHO‐free diet resulted in a large increase in TAG and NEFA versus the control diet; however, both were cleared by the following morning. A negative NEFA profile occurred with the control diet. Thus, mechanisms are present to restore lipid concentrations to their original AM concentrations daily. Fasting resulted in stable concentrations, except for a continuing increase in bHB. Glucose and insulin, common fuel regulators, could not explain the results.
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