In the long term, it all comes down to the quality of the carbohydrates consumed, not quantity. Diabetic patients are suggested to prefer nutrient-dense carbohydrate sources, such as vegetables, whole-grain products, and nuts, and to minimize the consumption of foods and beverages with added sugar.
Upcoming evidence suggests that meal planning and macronutrient distribution should be based on an individualized assessment of the subject’s medical and dietary history. In most patients with type 2 diabetes, caloric restriction, irrespective of any macronutrient adjustments, represents the best treatment option for weight loss and hence, diabetes remission.
Eventually, the adoption and maintenance of physical activity are critical for blood glucose management and overall health in individuals with type 2 diabetes and cardiovascular disease.
LCHF diets and weight loss
As stated before, LCHF diets have gained tremendous popularity among dieters over the last few years. Although capable of significant amounts of fat loss and weight loss, long-term LCHF diets do not seem to have any additional weight loss benefits compared to other types of diets. In other words, given a sufficient caloric deficit, the macronutrient ratio does not play such a significant role in weight loss. This concept is getting even more meaningful if we consider that the primary reason for the limited efficacy of dieting per se is poor adherence to dietary recommendations. In this case, LCHF diets, which admittedly are not enjoyable diets with reduced palatability because they lack entire food groups such as fruits, grains, and sweets, are unlikely to achieve and maintain a healthy body weight. Therefore, LCHF diets as a longer-term weight loss strategy are ineffective because most individuals find it challenging to adhere to them. Moreover, the longer term (>3 months) adoption of especially VLCDs, can result in dietary deficiencies of vitamins, minerals, and fiber and hence nutritional problems, such as constipation. Ultimately, our chosen diet should form an essential component of a healthy lifestyle with a proper caloric deficit and balance of all nutrients, which will be tailored to our preferences (pleasurable) and background (e.g., culture, work, family environment, etc.)
Contraindications of LCHF diets
LCHF diets may not be appropriate for all individuals. Pregnant or lactating women, people with or at risk of eating disorders, or people with type 2 diabetes and renal disease who want to adopt such a dietary pattern should opt for the third LCD category (45% carbohydrates of energy intake). Moreover, people with existing cardiovascular disease and an unfavorable lipid profile (high total and LDL cholesterol) should also not gravitate towards the VLCD category, which could potentially exacerbate their state through increased animal protein and fat consumption. Lastly, the evidence about the safety of LCHF diets in people with type 1 diabetes is minimal. As a result, this diet category is not included in the medical nutrition therapy recommendations for type 1 diabetes.
LCHF diets and exercise performance
Although LCHF diets may be challenging for the general population to adopt for a long time, athletes who are more disciplined and goal-oriented may be easier to stick to such a dietary pattern chronically. Is it worth it, or could there be setbacks in their training and performance? LCHF diets result in a metabolic shift in fuel availability and utilization, with increased fat oxidation and the production of ketones as an alternative fuel source when glycogen stores are low. Alternative energy sources in this state are also blood lactate and glucose derived from gluconeogenesis. In this metabolic process, non-carbohydrate sources, such as amino acids and lipids, constitute the substrate for glucose production. These adaptations do not seem to have detrimental effects on sports performance. However, there is one essential prerequisite for these metabolic adaptations to not only occur but also to set in without negatively impacting an athlete’s exercise performance. This prerequisite is the long-term adaptation to LCHF diets (fat-adaptation) which may take over a year for an athlete to perform at least equally as they used to on a high-carb diet. If an athlete is not fat-adapted, they are very likely to experience symptoms such as hypoglycemia, impaired exercise performance, and increased feelings of fatigue.
Despite the concept that endurance athletes require high-carb intakes to maintain sufficient muscle glycogen for high-intensity and endurance performance, there is emerging evidence that LCHF diets at least maintain, if not enhance, exercise performance in these kinds of sports. Endurance athletes who adapted to LCHF diets for 9-36 months (highly fat-adapted athletes) could reach the maximal fat oxidation rate at approximately 1.5g/min during progressive intensity exercise. They could also sustain fat oxidation rates exceeding 1.2g/min during exercise at ~ 65-70% VO2 max. This practically means that a highly fat-adapted endurance athlete could cover the energy cost of an Ironman Triathlon without needing to ingest exogenous carbohydrates. This contrasts with carb-adapted athletes who oxidize fat at 1.0g/min at the most and need to consume 90-105g/h of exogenous carbohydrates during prolonged exercise to maintain their performance. Hence, a long-term adaptation to LCHF diets allows for normal muscle glycogen content, utilization, and recovery. Actually, there is anecdotal evidence that rates of recovery are enhanced in highly fat-adapted endurance athletes.
Moreover, LCHF diets did have little effect on maximal aerobic capacity, rate of perceived exertion, and maximum heart rate of endurance athletes. However, RER was significantly reduced, indicating that more fat was involved in the energy supply and that endogenous carbohydrate sources (muscle and liver glycogen) would be retained for longer (glycogen-sparing effect) before they eventually get utilized for energy supply in ultra-endurance races. This metabolic adaptation may ultimately enhance exercise performance by giving highly fat-adapted athletes the potential to maintain higher relative exercise intensity during most of the distance while preserving muscle glycogen for sprints at the later stages of the competition.
Weight-class sports require athletes to maximize performance while carefully controlling their body weight to compete in a specific weight class with an optimum power-to-weight ratio. So, most athletes aim to reduce body weight for the competition transiently. LCHF diets are a rather useful weight-reducing strategy without compromising strength and power. They have the advantage of rapidly decreasing body weight without energy restriction, which could impair performance and lead to loss of muscle mass. This is accomplished through the reduction of stored glycogen and the accompanying loss of water which is stored along with glycogen (the storage of 1kg glycogen requires the storage of 3kg water). With carbohydrate restriction, an athlete could lose up to 2kg in a couple of days without compromising performance.
Apart from rapid weight loss purposes, even long-term exposure to an LCHF diet does not negatively affect muscle protein synthesis, and athletes engaging in resistance training programs can preserve their muscle strength by consuming such diets. In this direction, daily protein consumption of between 1.3-2.5g/kg is necessary to maintain muscle mass when following LCHF diets.
The exercise above 70% VO2max requires significant energy from the anaerobic metabolism. Hence, a single bout of short-term high-intensity exercise mainly utilizes energy from creatine phosphate and muscle glycogen breakdown (glycolysis). Field-based sports are examples of high-intensity exercise, where the ability to perform multiple sprints at the highest speed after short rests is crucial for game performance. Therefore, an elevated fat oxidation rate through an LCHF diet is unlikely to increase performance in such sports.
Long-term LCHF diets can have superior weight loss and metabolic health benefits compared to other dietary patterns, which are temporary though and, after the first year, equate with the effects of different diets. They are not for everyone, and specific population groups, like type I diabetics, are not recommended to follow them unless it’s under tight medical and dietary supervision. LCHF diets may be as effective or even more beneficial in many aspects of endurance performance through their increased fat oxidation and glycogen-sparing effects.