How Metabolic Flexibility Changes with Age

What metabolic flexibility is

Metabolic flexibility (MetFlex) is the capacity to shift between carbohydrate and lipid oxidation in response to nutrient availability [2]. It is assessed in research settings by measuring energy expenditure and fat oxidation, and by the response to a high-fat test meal, using gold-standard assessments of energy metabolism and body composition [1]. In the clinical research literature, reduced metabolic flexibility is described as a feature associated with obesity [2].

The work reviewed here centres on the sirtuin (SIRT) family — particularly SIRT1 and SIRT3 — and on the AMPK–PGC-1α–SIRT3 axis, which are implicated in mitochondrial biogenesis, energy expenditure, oxidative metabolism, and the regulation of insulin sensitivity [8][6].

Research Studies

Metabolic flexibility and extreme obesity in adults

A registered clinical study is evaluating energy metabolism (expenditure and fat oxidation) and metabolic flexibility in response to a high-fat test meal in 10 individuals with a BMI ≥60 kg/m² [1]. Participants are males and females aged 18–80 years, recruited from Baton Rouge, Louisiana, with a total participation duration estimated at approximately 10 days [1]. Exclusion criteria include major organ failure, uncontrolled endocrine disease, severe psychiatric illness, pregnancy, and inability to comply with study procedures [1]. This study is designed to characterise the phenotype in a specific, extreme-BMI adult population; it does not itself test an age effect.

Whole grape polyphenols and postprandial substrate shift

Grape polyphenols (resveratrol, catechins, quercetin, epicatechin) have been reported to enhance fat oxidation and mitochondrial function in laboratory and animal studies [2]. A registered trial is testing whether whole grape polyphenols shift postprandial substrate metabolism, integrating whole-room indirect calorimetry with high-resolution respirometry in peripheral blood mononuclear cells (PBMCs) [2]. The study rationale notes that whole grapes, rather than purified extracts, have not been tested for acute effects on MetFlex measured directly by whole-room calorimetry paired with mitochondrial function [2].

Mediterranean diet and metabolomic profiles in older adults with MCI

In a 24-week randomised controlled trial, changes in metabolomics profiles were analysed to assess the effects of a Mediterranean diet (MD), with and without probiotics, and a low-fat diet (according to World Health Organization recommendations) in 47 older adults aged ≥60 years (42.6% women) with mild cognitive impairment (MCI) [3]. The plasma metabolome was analysed using a quantitative LC-MS/MS targeted assay to assess metabolite changes derived from dietary intervention, and multivariate methods were employed to assess the impact of the diets on the plasma profile [3]. Interim findings from this trial link enhanced metabolic flexibility with cognition [3].

Sulforaphane and obesity-related metabolic dysfunction

A narrative review evaluates sulforaphane, a bioactive isothiocyanate derived primarily from broccoli and other cruciferous vegetables, in the context of obesity and obesity-related metabolic dysfunction [4]. The review describes obesity as characterised by adipose tissue dysfunction, insulin resistance, chronic low-grade inflammation, oxidative stress, mitochondrial dysfunction, and increased cardiometabolic risk, and notes that limitations related to cost, adverse effects, and long-term adherence have stimulated interest in complementary nutritional approaches [4]. Sulforaphane is described as having antioxidant, anti-inflammatory, and metabolic regulatory properties [4].

AMPK–PGC-1α–SIRT3 and aluminium exposure in HT22 cells

In mouse hippocampal neuronal HT22 cells exposed to aluminium maltolate [Al(mal)₃, 60–240 μM], aluminium exposure significantly increased senescence-associated β-galactosidase (SA-β-gal) activity and upregulated p16 and p21 expression, accompanied by G2/M phase arrest [6]. The study identifies the AMPK–PGC-1α–SIRT3 axis as mediating mitochondrial metabolic dysfunction and neuronal senescence in this in vitro model [6]. This is a cell-culture finding and does not establish an effect in humans.

Metformin withdrawal and metabolic flexibility in metabolic syndrome

A registered clinical trial is investigating how a short-term interruption of metformin treatment affects insulin sensitivity, glucose control, and metabolic flexibility in adults with metabolic syndrome who are taking metformin as part of their usual medical treatment [7]. The study rationale notes that temporary interruptions may occur in real-life situations, such as missed doses, medication access problems, travel, or planned short-term discontinuation for clinical reasons, and aims to understand whether stopping metformin for 14 days leads to rapid changes in glucose metabolism or whether the effects of previous metformin treatment may persist during a short period without the medication [7].

Sirtuin activators and weight management

A registered clinical study addresses the sirtuin (SIRT) family — particularly SIRT1 and SIRT3 — as a target due to its involvement in mitochondrial biogenesis, energy expenditure, oxidative metabolism, and the regulation of insulin sensitivity [8]. The study rationale notes that bioactive compounds that activate sirtuins, including nicotinamide riboside, are of growing interest in the context of metabolic flexibility and weight-management outcomes [8]. Obesity is described in that rationale as a chronic, multifactorial disease associated with a high burden of metabolic, cardiovascular, and psychosocial complications, and the long-term effectiveness of lifestyle-based weight-management strategies is described as remaining limited [8].

Chronic aflatoxin B₁ intake and glucose–lipid metabolism in ewes

In twenty non-pregnant, non-lactating multiparous Ghezel ewes assigned to either a control diet or the same basal diet supplemented with aflatoxin B₁-contaminated rice culture providing 500 µg AFB₁/kg dry matter for 40 days, AFB₁ reduced measures of rumen fermentation, hepatic health, oxidative stress, inflammation, and glucose–lipid metabolism [5]. Individual dry matter intake was not measured; however, all animals consumed the full daily ration, ensuring uniform nutrient intake [5]. This is an animal study in a ruminant model and is not directly translatable to human metabolic flexibility.

Comparison of selected models and populations

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Sources

• [1] Evaluating Metabolic Health in Individuals With Extreme Obesity — ClinicalTrials.gov
• [2] Vitis Intervention Trial in Substrate Metabolism — ClinicalTrials.gov
• [3] Enhanced metabolic flexibility links Mediterranean diet with cognition: interim findings from a randomized controlled trial. — europe_pmc
• [4] Sulforaphane and Broccoli-Derived Preparations in Obesity and Obesity-Related Metabolic Dysfunction: Mechanistic Insights, Preclinical Evidence, and Clinical Perspectives. — europe_pmc
• [5] Impact of chronic dietary aflatoxin B1 intake on rumen fermentation, hepatic health, oxidative stress, inflammation, and glucose-lipid metabolism in fat-tailed ewes. — europe_pmc
• [6] The AMPK-PGC-1α-SIRT3 axis mediates mitochondrial metabolic dysfunction and neuronal senescence induced by Al(mal)3 exposure in HT22 hippocampal neuronal cells. — europe_pmc
• [7] Metformin Withdrawal In Metabolic Syndrome — ClinicalTrials.gov
• [8] Sirtuin Activators and Weight Loss — ClinicalTrials.gov
• [9] Mitokines as bioenergetic stress signals in cardiovascular disease: mitochondrial communication, endocrine adaptation, and translational implications. — europe_pmc (reference only)
• [10] HACD1-driven long-chain fatty acid metabolic reprogramming enhances esophageal cancer tumorigenicity. — europe_pmc (reference only)