Hypothesis: Improvements in aerobic capacity and injury recovery might be achieved by nutritional strategies specifically targeted at improving mitochondrial function by both enhancing mitochondrial biogenesis and recycling dysfunctional proteins by autophagy.
Endurance performance is closely predicted by oxygen consumption at the anaerobic (or lactate) threshold (VO2LT) and VO2LT is proportional to muscle mitochondrial volume. The evidence for mitochondrial function being the performance limiting factor at or above the anaerobic threshold is that lactate is generated from exercising muscle in spite of adequate blood supply and oxygen availability and therefore “anaerobic threshold” is something of a misnomer and Lactate Threshold (LT) would be a more accurate term. Lactate is generated due to rapid increase in ADP/ATP ratio from working muscle. The increased ADP levels must be converted to ATP within mitochondria by the ATP synthase protein complex associated with the Electron Transport Chain and no matter how much oxygen is being transported to the muscle conversion of ADP to ATP is limited by the amount of functioning ATP synthase molecules in the exercising muscle.
Experience athletes will be very familiar with how much effort and work rate they can sustain at and above their LT as exceeding LT for brief periods during endurance performance quickly leads to hyperventilation and exhaustion.
While VO2max is vitally important to athletic ability it is a relatively stable attribute of athletes, however VO2LT and the ratio of VO2LT/VO2max are better indicators of ability in endurance sports (1) and is also more responsive to training.
VO2LT is essentially maximum sustainable Aerobic Enzyme Activity and is dependent on mitochondria number and enzyme density. Muscle biopsy studies in humans have shown mitochondria are highly responsive to exercise and can increase with 6-8 weeks of training and decrease within 6-8 weeks of detraining (2). Peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) is the master controller of mitochondrial biogenesis and is in turn controlled by both physical activity and nutrition (3).
Attempts at improving athletic performance in humans and animals through various dietary modifications have been tried before with varying results. Traditionally high carbohydrates were in vogue but more recently attempts at stimulating fat metabolism in order to spare glycogen stores have been tried. In summary low carbohydrate/high fat interventions over several weeks, were more effective than interventions over days and tests of endurance were improved more than tests of sprints, but it is fair to say that there have been few if any deteriorations in endurance performance in studies on high fat diets as long as sufficient time for adaptation was allowed (4). There have been no studies with the specific goal of monitoring VO2LT, the physiological parameter that is closely linked to mitochondrial biogenesis. Two recent studies document greater mitochondrial enzyme enhancement while training in fasted (2) and glucose withheld conditions (5) but with no dietary change between training sessions. The most up to date review by the Australian group (4) used short term high fat diets that still had substantial carbohydrate content and therefore were unlikely to create conditions for enhanced mitochondrial biogenesis.
“Train Low perform High” This catch phrase has been used to guide the concept of fat enhancement during training, the idea is to train on a low carb/ketogenic diet and high carb load only 24 hours or so before a competitive event.
- The suggested diet for individual athletes to be test should be enjoyable and encompass most of what is already known to be beneficial but with a strict avoidance of hyperglycemia inducing a mild ketogenic state by replacing high glycemic carbohydrates with plant foods high in fiber water and phytonutrients. Protein of not more than 2 gm/kg/day from meat, fish, poultry, eggs, dairy and the bulk of food consumed from unlimited amounts of fruits, nuts, vegetables, salads, oils and dressings with lots of herbs and spices. In this way relatively large and satisfying meals would supply the majority of calories from slowly digested carbohydrates, fats, oils and short chain fatty acids from prebiotic fiber fermentation.
- Carbohydrate restoration for competitive events can be achieved by increasing carbohydrate intake 1 day prior to competition in order to increase muscle glycogen content.
- Improvement should not be expected in less than 4 weeks, neither should significant performance improvement occur during training because muscle glycogen will be depleted on a ketogenic diet, however muscle proteins that generate energy from fat oxidation should gradually increase ultimately resulting in glycogen sparing and greater endurance performance.
Cell Signalling Pathways controlling mitochondrial function
- Hyperglycemia and insulin suppress PGC1 by Akt/PKB removing fox01 from the PGC1 promoter.
- Glucose produces ATP & NADH through extra-mitochondrial glycolysis; decreases cytosol NAD+ inhibits SIRT1 which activates PGC1 through deacetylation Fig 2.
- A mild ketogenic state brought about by low dietary glucose availability increases PGC1, via glucagon action and direct effects of changes in free fatty acid levels (FFA) and ketone bodies on nuclear gene transcription.
- Insulin profoundly suppresses FFAs which are ligands for several transcription factors (PPARs & Free Fatty Acid Receptors) that interact with PGC1 in the promotion of mitochondrial protein synthesis.
Energy Production, mitochondrial recycling and cell maintenance
Mitochondria are constantly destroyed and re-synthesized with estimates in rats for half-lives in; liver, 9.3 days; testes, 12.6; heart, 17.5 and brain 24.4 days (6). Cell proteins are broken down by proteasomes (7) and whole organelles by autophagy. Mitochondrial mass is increased through biogenesis rather than decreasing mitophagy (8) which is necessary for cell maintenance as blocking autophagy accelerates apoptosis and prevents the life extension and metabolic improvements associated with calorie restriction and sirtuins. (9) (10) (11).
The likely mechanisms whereby mitochondrial function is controlled through substrate and hormone levels are described in a review by Douglas Wallace (10): Very simply high glucose and insulin levels inhibit mitochondrial biogenesis while it is stimulated by glucagon, fatty acids and ketone bodies (12). There is a sea change in nuclear signaling inside cells that pivots around the abundance of glucose. Glycolysis takes place in cytosol producing higher NADH/NAD+, whereas fatty acids and ketone bodies are metabolized in mitochondria and thus increase cytosolic NAD+ which activates SIRT1, a deacetylase which counteracts the acetylation and consequent deactivation of FOXO and PGC1. The controlling effect of glucose on pancreatic secretion of either insulin or glucagon is another pathway regulating mitochondrial biogenesis through the master controller PGC1 as shown in the figure below (13). In addition the intensity of physical activity directly increases PGC1 transcription in muscle cells and increases sympathetic tone suppressing insulin and increasing glucagon pancreatic secretion, both glucagon and adrenergic receptors activate the cAMP-PKA mediated increase in PGC1 transcription (13) (14) (10).
Regulation of PGC-1 Promoter Activity by Protein Kinase B and the Forkhead Transcription Factor FKHR.
Daitoku, Hiroaki; Yamagata, Kazuyuki; Matsuzaki, Hitomi; Hatta, Mitsutoki; Fukamizu, Akiyoshi
Diabetes. 52(3):642-649, March 2003.
Transcriptional regulation of the PGC-1 promoter by FKHR and CREB. A schematic model for PGC-1 gene transcription mediated by FKHR (FOXO) and CREB through each responsive element via different hormone signals. Left: insulin activates PI3 kinase signaling pathway, which stimulates phosphorylation of FKHR by PKB (Akt), followed by nuclear exclusion and repression of PGC-1 gene transcription. Right: Glucagon activates cAMP signaling pathway, which stimulates phosphorylation of CREB by PKA, and thereby induces the expression of PGC-1. (13)
Ketogenic Diets Stimulate Systemic Mitochondrial Biogenesis
The Ketogenic Diet was designed in the 1920’s as a starvation mimicking diet, since starvation was known to limit seizures (15). The classical KD; high fat, very low carbohydrate, was an effective treatment for epilepsy but fell out of favor with the development of phenytoin in 1938 but has experienced a resurgence in use over the past 20 years, particularly in the treatment of refractory epilepsy (16). Less rigid versions of the classical KD have been used with equal efficacy such as the low glycemic treatment (17) and modified Atkins diet (18). Not only are seizures decreased in children with epilepsy but improvements were noted in behavior and cognitive functions (16) (19) (20). A great deal of research has gone into the mechanisms involved and widespread improvements in energy metabolism have been documented (21). Mitochondria from animals fed a ketogenic diet produced less reactive oxygen species (ROS), mitochondrial density increased and numerous proteins involved in oxidative phosphorylation increased in the hippocampus in addition to anti-apoptosis mechanisms (20). Neuroprotective effects of a KD have been reported in Parkinson’s disease and Alzheimer’s disease (20). Improvements in Autism have been reported (22) and this is not surprising given the links between Autism, ADHD and mitochondrial dysfunction (23) (24) (25).
The benefits of ketogenic diets are not confined to nerve tissue similar improvements in mitochondrial function have been documented in muscle (26), heart (27) and liver (28) and there is a systemic increase in mitochondrial and antioxidant enzymes brought about by PGC1 and NRF2 (nuclear respiratory factor) (28).
The ketogenic diet has also been used very effectively for weight loss for at least 100 years (29) and popularized by the Atkins Diet in the 1970’s. Atkins was demonized by the medical establishment of the time because he was advocating a high fat diet that was thought to increase the risk of cardiovascular disease. However, epidemiologic studies, controlled trials and basic science investigations over the last 10 years have shown that ketogenic and carbohydrate restricted diets actually improve both CVD risk factors and outcomes (30) (31) (32) (33) (34) (10) (14). Objections to the classical ketogenic diet due to palatability, lipid profile and complications such as constipation can be overcome by consuming the bulk of one’s food in the form of low glycemic plant foods that have a high water, fiber and phytonutrient content but low glucose availability (31) (35) such as “Eco-Atkins” (36) and a Spanish Ketogenic Mediterranean diet (37) resulting in dramatic improvements in lipid profiles over control diets containing more carbohydrates. (38) (39)
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