Saturday, 1 June 2013

Metabolic Inflexibility: What it really means.

Here's a picture from Metabolic Flexibility and Insulin Resistance.

The Metabolically-Inflexible (MI) & Insulin Resistance

Here's another picture.
Fig 2. ● = Metabolically-Flexible (MF). ○ = Metabolically-Inflexible (MI).
Salient points:
1) Excess serum FFA a.k.a. NEFA is bad.
2) Respiratory Quotient (RQ) a.k.a. Respiratory Exchange Ratio (RER) changes due to dietary changes are more sluggish in the MI than in the MF.
3) Under Insulin Clamp conditions, RQ/RER is lower in the MI than in the MF, due to impairment of glucose oxidation and non-oxidative glucose disposal.

I have posted this because of Danny Roddy's post Is Supplemental Magnesium A Surrogate For Thyroid Hormone? , which leads onto A Bioenergetic View of High-Fat Diets.

In the first article, Danny Roddy writes:-
"Additionally, taking magnesium while actively engaging in a diet or lifestyle that reduces the respiratory quotient (e.g., high-fat diet, light deficiency, excessive exercise) seems pretty silly. For example, as a rule, diabetics have a reduced respiratory quotient (Simonson DC, et al. 1988), tend to have higher levels of free fatty acids or NEFA (Kahn SE, 2006), and are often deficient in magnesium (De Valk HW, 1999)."

The second sentence (diabetics have a reduced respiratory quotient...and are often deficient in magnesium) seems to contradict the first sentence (...taking magnesium while actively engaging in a diet or lifestyle that reduces the respiratory quotient seems pretty silly).

Simonson DC, et al. 1988 is Oxidative and non-oxidative glucose metabolism in non-obese type 2 (non-insulin-dependent) diabetic patients.
"In conclusion, during the postabsorptive state and under conditions of euglycaemic hyperinsulinaemia, impairment of glucose oxidation and non-oxidative glucose disposal both contribute to the insulin resistance observed in normal weight Type 2 diabetic patients. Since lipid oxidation was normal in this group of diabetic patients, excessive non-esterified fatty acid oxidation cannot explain the defects in glucose disposal."

Impaired glucose oxidation with normal lipid oxidation lowers RQ/RER. Therefore, lower RQ/RER must be bad, right? Wrong. From the above study:-
"...euglycaemic insulin clamp studies were performed..."
Remember Salient point 3)? Simonson DC, et al. 1988 is an insulin clamp study, the results of which don't apply to free-living people (who aren't insulin clamped).

See also Determinants of the variability in respiratory exchange ratio at rest and during exercise in trained athletes. RER/RQ increases & decreases with increases & decreases in exercise intensity. This is Metabolic Flexibility (MF). Sorry, Danny.

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