Nutritional Ketosis and Mitohormesis: Potential Implications for Mitochondrial Function and Human Health

Abstract

Impaired mitochondrial function often results in excessive production of reactive oxygen species (ROS) and is involved in the etiology of many chronic diseases, including cardiovascular disease, diabetes, neurodegenerative disorders, and cancer. Moderate levels of mitochondrial ROS, however, can protect against chronic disease by inducing upregulation of mitochondrial capacity and endogenous antioxidant defense. This phenomenon, referred to as mitohormesis, is induced through increased reliance on mitochondrial respiration, which can occur through diet or exercise. Nutritional ketosis is a safe and physiological metabolic state induced through a ketogenic diet low in carbohydrate and moderate in protein. Such a diet increases reliance on mitochondrial respiration and may, therefore, induce mitohormesis. Furthermore, the ketone β-hydroxybutyrate (BHB), which is elevated during nutritional ketosis to levels no greater than those resulting from fasting, acts as a signaling molecule in addition to its traditionally known role as an energy substrate. BHB signaling induces adaptations similar to mitohormesis, thereby expanding the potential benefit of nutritional ketosis beyond carbohydrate restriction. This review describes the evidence supporting enhancement of mitochondrial function and endogenous antioxidant defense in response to nutritional ketosis, as well as the potential mechanisms leading to these adaptations.

Figure 1

β-hydroxybutyrate and, in some cases, acetoacetate contribute to protection against oxidative stress by decreasing production of mitochondrial reactive oxygen species (mtROS), by increasing expression or protein content of antioxidant enzymes through histone deacetylase (HDAC) inhibition, and by directly scavenging the hydroxyl radical (^•OH). Upregulation of antioxidant enzymes through HDAC inhibition includes manganese superoxide dismutase (SOD2), catalase, and metallothionein II and is likely mediated by the transcription factor forkhead box O 3a (FOXO3a).

Figure 2

Nutritional ketosis may initiate bioenergetic and mitohormetic signaling through an increase in catecholamines or adiponectin, a decrease in insulin or glycogen, or an increase in β-oxidation that leads to an increase in mitochondrial reactive oxygen species (mtROS) or NAD⁺. This leads to further signaling involving AMP-activated protein kinase (AMPK), silent mating type information regulation 2 homologue 1 (SIRT1), peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α), forkhead box O 3a (FOXO3a), and nuclear factor erythroid-derived 2-like 2 (NFE2L2), ultimately leading to transcription of genes related to oxidative capacity, mitochondrial uncoupling, and antioxidant defense. These adaptations collectively contribute to resistance against oxidative stress. Other proteins involved include liver kinase B1 (LKB1), which activates AMPK; nicotinamide phosphoribosyltransferase (NAMPT), which facilitates SIRT1 activation through NAD⁺ synthesis; and nuclear respiratory factors 1 and 2 (NRF-1 and NRF-2) and mitochondrial transcription factor A (TFAM), which promote mitochondrial biogenesis.