Fat fasting is a specialized, short-term dietary intervention primarily used by individuals already following a ketogenic or very low-carbohydrate eating plan. It is a temporary strategy designed to manipulate the body’s metabolism through extreme macronutrient restriction. This approach is not a sustainable long-term diet but a tool employed to achieve a specific, immediate metabolic effect: quickly forcing the body into a deeper state of nutritional ketosis.
Defining the Fat Fast Protocol
The fat fast is defined by a severe limitation in total calories and non-fat macronutrients. Participants typically consume between 1,000 and 1,200 calories per day, regardless of body size or activity level. The defining factor is the macronutrient distribution: 80% to 90% of daily calories must come from fat.
A standard ketogenic diet usually allows for 65% to 90% fat, 10% to 30% protein, and less than 5% carbohydrates. The fat fast dramatically lowers the protein and carbohydrate allowance, often resulting in less than 10% of total calories coming from these combined sources. This restricted intake, coupled with the low calorie count, rapidly depletes the body’s glycogen stores. The metabolic rationale is that the near-zero carbohydrate load forces the liver to quickly increase the production of ketone bodies from fatty acids. The high fat content ensures a ready supply of fuel, while the calorie deficit encourages the burning of stored body fat.
Practical Implementation: Meal Planning and Duration
Executing a fat fast requires careful selection of foods to meet the strict fat-to-calorie ratio while keeping protein and carbohydrates negligible. Common food choices center on pure fats, high-fat dairy, or oils.
Food Choices
These often include coconut oil, medium-chain triglyceride (MCT) oil, butter, cream cheese, macadamia nuts, avocados, and high-fat fish like salmon or sardines. Small, high-fat meals are usually consumed throughout the day, often broken into four or five portions of 200 to 250 calories each. Some individuals prepare “fat bombs,” which are small, dense snacks designed to deliver a high dose of fat in a small volume.
Duration
This dietary pattern is intended to be short-lived. It is strongly recommended that the fat fast only be followed for a maximum of two to five days. Extending this period is discouraged due to the lack of micronutrients and protein, which risks muscle wasting and nutrient deficiencies.
The Goal: Accelerating Ketosis and Breaking Plateaus
Individuals undertake the fat fast primarily for two metabolic outcomes related to ketogenic dieting.
Accelerating Ketosis
The first goal is to rapidly establish or deepen nutritional ketosis. This is useful for those new to a low-carbohydrate lifestyle or for individuals who have temporarily consumed too many carbohydrates, effectively “kicking” them out of ketosis. The restrictions quickly deplete the body’s glucose reserves, prompting the liver to accelerate ketone production to fuel the brain and body.
Breaking Plateaus
The second objective is to break through a weight loss plateau, a common experience during long-term calorie-restricted diets. The fat fast is theorized to “reset” the body’s metabolism by providing a temporary, aggressive shift in fuel source and calorie intake. The increased presence of ketones, specifically beta-hydroxybutyrate, is also thought to have anti-inflammatory effects that may improve the signaling of appetite-regulating hormones like leptin. By inducing a short, sharp caloric shock, the diet aims to signal that the body must rely solely on fat for energy, potentially restarting the stalled weight loss process.
Potential Drawbacks and Health Warnings
Despite the intended metabolic benefits, the fat fast carries significant risks and is associated with several side effects. The lack of dietary variety and low protein intake can quickly lead to micronutrient deficiencies and increase the risk of muscle loss. Many individuals experience an intensification of “keto flu” symptoms, including headaches, dizziness, fatigue, and irritability. Gastrointestinal distress, such as diarrhea or constipation, is common due to the sudden, high intake of fat and low fiber content.
This protocol is not suitable for everyone and necessitates medical consultation before beginning. Individuals with pre-existing conditions such as gallbladder disease, pancreatitis, or liver disorders should avoid a fat fast due to the high fat load. The diet is also not recommended for pregnant or breastfeeding individuals, or those with a history of eating disorders. People with Type 1 or Type 2 diabetes must exercise extreme caution and should not undertake this diet without strict medical supervision, as it can cause dangerous fluctuations in blood sugar and insulin levels.