Cardiovascular diseases (CVD) are often linked to unhealthy lifestyles, including poor dietary habits, alcohol consumption, smoking, and low physical activity levels. Consequently, preventing CVD requires managing risk factors like impaired lipid and glycemic profiles, high blood pressure, and obesity through healthy lifestyle interventions. Different dietary recommendations often emphasize increasing or avoiding entire food classes, with consequences on overall health that are not always fully understood or foreseeable.
Introduction to Low-Carbohydrate Diets
In recent years, the ketogenic diet (KD) has emerged as a potentially effective lifestyle intervention for metabolic syndrome. While its benefits for weight loss and glucose metabolism are relatively well-established, the long-term effects of KD on physical performance and blood pressure (BP) levels, particularly in individuals with and without hypertension, remain less clear.
A ketogenic diet (KD) is characterized by a high-fat intake (55-90% of calories), adequate protein (30-35% of daily caloric requirement, with a minimum of 1 g/kg of protein), and very low carbohydrate intake (5-10% of total calories, typically less than 50 g/day). By drastically reducing carbohydrate intake, the body undergoes a metabolic shift, depleting glycogen reserves and transitioning to gluconeogenesis and ketogenesis. This shift results in the production of ketone bodies, which can be efficiently utilized by the heart, muscles, brain, and kidneys for energy production.
It's important to note that there isn't a single, universally defined "KD" protocol. Various approaches exist, differing in carbohydrate restriction levels, protein contribution, and the type of fat consumed (animal versus vegetable). These variations can lead to different metabolic consequences. Moreover, KDs fall under the broader category of low-carbohydrate diets (LCDs), which encompass a diverse range of nutritional regimens with a common denominator of reduced carbohydrate content. Examples of LCDs include the Atkins diet, the Zone diet, the South Beach diet, and the Paleo diet.
Ketogenic Diet and Metabolic Changes
Given that the average daily macronutrient intake in many populations includes at least 45% carbohydrates, an LCD is generally defined as a diet providing between 50 and 150 g of carbohydrates per day (10-30% of total calories). A KD, in contrast, typically restricts carbohydrate intake to less than 50 g per day (less than 10% of total calories), with some protocols limiting it to below 20 g per day.
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The scientific community has shown increasing interest in KD for its potential in combating the obesity epidemic, as well as other conditions like diabetes mellitus and cardiovascular diseases (CVDs). These conditions often stem from poor dietary habits and sedentary lifestyles. KD induces a metabolic state similar to starvation, where the body initially relies on glycogen reserves for energy. When these reserves are depleted, gluconeogenesis is stimulated to produce glucose from sources like lactic acid, glycerol, and amino acids. If gluconeogenesis is insufficient, ketone bodies are produced as an alternative energy source, utilizing dietary fat and fat stored in adipose tissue.
Short- to Medium-Term Effects of Ketogenic Diets
A KD is typically followed for a period ranging from a few weeks to several months. Research indicates that KD, sometimes referred to as a very low carbohydrate diet (VLCD) or very low carbohydrate ketogenic diet (VLCKD), can be effective in the short to medium term (three to six months) for managing lipid profiles and combating obesity. This can lead to significant reductions in weight, body mass index (BMI), and fat mass. However, there is limited data on long-term weight loss maintenance. Studies have reported selective reductions in visceral fat with very low carbohydrate ketogenic diets.
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