What Is a Fat Fast and Is It Healthy?

Written and medically reviewed by Katya Meyers, RD

Fat fasting is a dietary technique geared towards weight loss and other health reasons. Those who use fat fasting claim that it allows them to break through weight-loss plateaus, lose weight quickly, or get into ketosis without hunger or food cravings. 

But are fat fasts necessary for weight loss? And are they healthy in the first place? Read on for a scientific breakdown.

What Is a Fat Fast?

A fat fast is a short-term dietary approach that involves consuming high amounts of healthy fats while severely restricting carbohydrates and protein intake. During a fat fast, the macronutrient ratio is typically shifted so that 80–90% of an individual’s daily calories come from healthy fats, with very limited amounts of carbohydrates and protein, similar to a ketogenic diet. The goal is to induce a state of ketosis, where the body relies primarily on fat for energy instead of carbohydrates.

The duration of a fat fast can vary, but it is typically followed for a short period, ranging from a few days to a week. It is important to note that a fat fast is not meant to be a long-term or sustainable diet plan but rather a temporary strategy to kick-start weight loss or break through a weight-loss plateau.

Is Fat Fasting Healthy?

A fat fast is a dietary approach that involves consuming high amounts of fats while severely restricting carbohydrates and protein intake. While it may lead to weight loss in the short term, it is not considered a healthy or sustainable long-term strategy. While fats play essential roles in the body, such as providing energy and supporting hormone production, a healthy diet should include a balanced combination of macronutrients, including minimally processed carbohydrates and proteins.

Carbohydrates provide important nutrients, such as fiber, vitamins, and minerals, while proteins maintain and repair muscle function. A well-rounded and nutritious diet should prioritize whole foods, including a variety of fruits, vegetables, lean proteins, whole grains, and healthy fats in appropriate proportions.

Before considering a fat fast, consult with a healthcare professional or registered dietitian to ensure a period of high-fat consumption geared towards weight loss aligns with your individual health needs and goals.

Fat Fasting vs. Other Types of Fasting

By now, you have likely heard about fasting and may be wondering if fasting is right for you. Many types of fasting exist and have proven to be effective for losing weight, reducing inflammation, enhancing cell autophagy, and increasing insulin sensitivity — all of which can help you live a longer, healthier life

Intermittent fasting is one of the most common types of fasting, and it involves condensing your eating window to allow for spontaneous calorie deficits and help your body become more “metabolically flexible” — in other words, being able to shift easily from using carbohydrates to fats for fuel, including your own fat stores. Many people begin intermittent fasting because it is often an effective strategy for weight loss, but it is important to remember weight is not the only marker of improved health. However, if weight loss is your goal and you are not seeing results, try switching up factors such as the duration of your fast and the composition of what you are eating during your eating window.

Although it is not a true fast, a fat fast does have some metabolic similarities to other types of fasting. Similar to fasting, a fat fast forces the body to burn through its limited supply of stored glucose before relying more heavily on fat for fuel. As fat burning begins, the body makes the “metabolic switch” into ketosis, where the liver converts fat to ketones. While this does increase the percentage of fat being used for fuel, it is important to remember that you do not have to be in ketosis to lose weight.

In contrast to carbohydrates or protein, fat has virtually no impact on blood sugar and insulin levels and therefore doesn’t interfere with fasting metabolism. So, a “fat fast” may mimic fasting as far as your metabolism can tell, but the fat you are consuming is displacing the need to burn body fat.

What Can You Eat on a Fat Fast?

The inclusion of small amounts of protein and carbohydrates is allowed on a fat fast, meaning it is not straight oil or fats, since those are the only food products that are truly 100% fat. However, it is still restrictive in terms of the types of foods allowed — most fat-fasting protocols recommend that 80–90% of calories come from fat. 

Foods to Eat on a Fat Fast

During a fat fast, the primary focus is on consuming foods that are high in healthy fats while minimizing carbohydrates and protein intake.

Here are some examples of foods that can be included in a fat fast:

  • Avocados: Rich in monounsaturated fats, avocados are a great source of healthy fats. They can be enjoyed on their own, added to salads, or used to make guacamole.
  • Olive oil: This oil is a staple of Mediterranean cuisine and is high in monounsaturated fats. Use it as a dressing for salads or drizzle it over cooked vegetables.
  • Coconut oil: A great source of medium-chain triglycerides (MCTs), coconut oil can be used in cooking or added to smoothies for an extra boost of healthy fats.
  • Butter and ghee: These dairy products are high in saturated fats and can be used for cooking or as spreads. Opt for grass-fed or organic varieties if possible.
  • Nuts and seeds: Almonds, walnuts, macadamia nuts, chia seeds, flaxseeds, and hemp seeds are all excellent sources of healthy fats. High-fat nuts and seeds can be eaten as a snack or added to salads and low-carb recipes.
  • Fatty fish: Salmon, mackerel, sardines, and trout are examples of fatty fish rich in omega-3 fatty acids. Include them in your fat fast by grilling, baking, or poaching them.
  • Full-fat dairy: Choose full-fat options like cheese, cream, and unsweetened Greek yogurt for an easy way to incorporate healthy fats into your diet.

Foods to Avoid on a Fat Fast

During a fat fast, it’s recommended to avoid or significantly limit certain foods that are high in carbohydrates and protein in favor of foods with a lot of fat.

Here’s what to avoid:

  • Grains and starches: This includes bread, pasta, rice, cereals, and other grain-based products. These foods are rich in carbohydrates and should be avoided during a fat fast.
  • Sugary foods: This includes sugary drinks, candies, desserts, and sweetened snacks. They are high in carbohydrates and can hinder the fat-burning process.
  • Fruits: While fruits are generally considered healthy, they also contain natural sugars and carbohydrates. During a fat fast, it’s best to limit or avoid fruits to minimize carbohydrate intake.
  • Legumes and beans: Beans, lentils, chickpeas, and other legumes are carbohydrate-rich foods and should be avoided during a fat fast.
  • High-carb vegetables: Some vegetables, such as potatoes, carrots, and corn, are higher in carbohydrates compared to others. Limit or avoid these vegetables during a fat fast.
  • High-protein foods: While proteins are essential for a balanced diet, during a fat fast, it’s important to restrict protein intake to encourage the body to rely on fat as a fuel source. Avoid or minimize consumption of meats, poultry, fish, eggs, and dairy products.

Sample Fat-Fast Meal Plan

This is an example of what a one-day fat-fast meal plan might look like; however, specifics can vary, based on your individual preferences, dietary restrictions, and nutritional needs. 

  • Breakfast: Bulletproof-style butter coffee. Blend 1 cup of freshly brewed coffee with 1 tablespoon of coconut oil and 1 tablespoon of grass-fed butter or ghee.
  • Snack: Handful of macadamia nuts, which are high in healthy fats and low in carbs.
  • Lunch: Mixed-green salad with avocado. Combine a variety of leafy greens (such as spinach, arugula, and kale) and top with sliced avocado. Drizzle with olive oil and sprinkle with salt and pepper.
  • Snack: Celery sticks with almond butter. Spread a tablespoon of almond butter onto celery sticks for a crunchy and satisfying snack.
  • Dinner: Grilled salmon with steamed broccoli. Grill a salmon filet seasoned with herbs and spices of your choice. Serve it with a side of steamed broccoli drizzled with olive oil.
  • Snack: Full-fat Greek yogurt. Enjoy a small portion of unsweetened, full-fat Greek yogurt for a creamy and protein-rich snack option.

Lastly, don’t forget to drink plenty of water throughout the day to stay hydrated.

Potential Benefits of a Fat Fast

A fat fast is believed to offer several potential benefits, although it’s important to note that scientific research specifically on fat fasting is limited. Here are some potential benefits that proponents of fat fasting suggest.

Weight Loss and Overcoming a Weight-Loss Plateau

A fat fast is sometimes used as a short-term strategy to break through a weight-loss plateau. The idea behind it is to shift the body’s fuel source from carbohydrates to fats, potentially promoting fat burning. However, it’s important to note that the effectiveness of a fat fast for overcoming a weight-loss plateau can vary from person to person, and has not been sufficiently researched. 

Weight-loss plateaus can occur for various reasons, such as metabolic adaptations, hormonal changes, or inconsistencies in calorie intake or exercise. While a fat fast may provide a temporary boost in weight loss due to the caloric restriction and increased fat burning, it’s not a sustainable long-term solution.

To overcome a weight-loss plateau, it’s crucial to focus on holistic strategies that promote overall health and sustainable weight management. Other strategies to incorporate include food journaling, moving more throughout your day, managing stress, intermittent fasting, and making sure you are getting enough sleep.

Boosting Metabolism

While a fat fast may increase fat burning temporarily, it is not typically considered an evidence-based strategy for boosting metabolism. Metabolism refers to the complex process by which your body converts food into energy. Several factors, such as age, genetics, body composition, and activity level influence your metabolism. The impact on metabolism is not well-studied or understood, and the long-term effects of a fat fast on metabolism are uncertain.

Sustainable methods for boosting metabolism include:

  • Strength training: Building muscle mass through strength-training exercises can increase your basal metabolic rate (BMR) as muscles require more energy at rest compared to fat.
  • Regular physical activity: Engaging in regular physical activity, including cardiovascular exercises and high-intensity interval training (HIIT), can help increase your overall energy expenditure and potentially boost metabolism.
  • Eating enough protein: Protein has a higher thermic effect of food compared to carbohydrates or fats, meaning your body burns more calories during the digestion and absorption process. Including adequate protein in your diet can help support metabolism.
  • Eating enough calories: Severe calorie restriction or prolonged fasting can actually slow down your metabolism as your body adapts to conserve energy. It’s important to consume enough calories to support your body’s needs.
  • Staying hydrated: Drinking enough water can support optimal metabolic function. Dehydration can negatively impact your metabolism.
  • Getting enough sleep: Lack of sleep can disrupt hormones that regulate metabolism. Aim for quality sleep to support overall metabolic health.

Remember, everyone’s metabolism is unique, and there are no magic solutions for significantly boosting metabolism. Focusing on healthy lifestyle habits, including a balanced diet, regular exercise, and adequate sleep, is key for supporting a healthy metabolism.

Enhancing Ketosis

By limiting carbohydrate intake, the body shifts its primary fuel source from glucose to ketones, which are produced from fat breakdown. This can be advantageous for individuals aiming to achieve nutritional ketosis and the associated benefits it may offer, or those looking to rapidly re-enter ketosis after a “cheat day.” Some proponents also argue that a fat fast can help the body become more efficient at using fat for fuel, potentially enhancing metabolic flexibility, making it easier to complete other types of fasts, and, most importantly, improving your overall metabolic health. 

Reducing Appetite

The high fat content of a fat fast can help promote feelings of satiety and reduce hunger, potentially leading to lower calorie intake.

Potential Risks of a Fat Fast

While a fat fast may have potential benefits, it’s important to consider the potential risks and drawbacks associated with this approach. Here are some potential risks of a fat fast:

Nutrient Deficiencies

Severely restricting carbohydrates and protein while primarily relying on fats can lead to inadequate intake of essential nutrients, including vitamins, minerals, and fiber. This can increase the risk of nutrient deficiencies and impact overall health and well-being.


​​Excessively high fat intake with minimal carbohydrates and protein may lead to an imbalance in macronutrients, resulting in fatigue and other side effects. Carbohydrates and protein play important roles in providing energy, supporting muscle maintenance, and fulfilling various physiological functions. Lack of these nutrients in the long term can have negative effects on overall health and energy.

Rebound Weight Gain

Following a fat fast can be challenging due to the limited food options and restrictions on carbohydrates and protein. This can make it difficult to sustain the diet over an extended period, potentially leading to a return to old eating habits and weight regain.

How to Do a Fat Fast Safely

If you decide to pursue a fat fast, it’s important to prioritize safety and ensure you approach it in a responsible manner. Before starting a fat fast or any significant dietary change, consult with a healthcare professional or registered dietitian. They can evaluate your health history, current condition, and advise you on whether a fat fast is suitable for you.

If you do decide to proceed, keep in mind that a fat fast is intended to be a short-term approach, typically lasting a few days to a week — prolonged or repeated fat fasting can have negative health implications. Be sure to drink enough water, monitor electrolytes, and choose healthy sources of fat. Remember, a fat fast is an extreme dietary approach and may not be suitable or necessary for everyone.

Macronutrient Breakdown    

The majority of these calories will come from healthy fats, such as avocados, coconut oil, olive oil, nuts, and seeds. The fat content should be high, making up around 80-90% of your total calorie intake during the fat fast.

Duration of a Fat Fast

A fat fast is intended to be a short-term approach, typically lasting a few days to a week. Prolonged or repeated fat fasting can have negative health implications and is not recommended. 

Calorie Recommendations

Calorie intake during a fat fast can vary depending on individual factors such as gender, age, weight, activity level, and specific goals. However, a general guideline for calorie intake during a fat fast is typically around 1,000–1,200 calories per day. It’s important to note that this is a rough estimate and should be adjusted based on individual needs and preferences.

Work with Your Healthcare Professional

Remember, before making any significant dietary changes, you should consult your healthcare professional. 

Who Should Try a Fat Fast

A fat fast is a specialized dietary approach that should be approached with caution. It is typically considered more extreme than a standard low-carbohydrate, high-fat (LCHF) or standard ketogenic diet.

A fat fast may be appropriate for individuals who are already adapted to a classic keto diet or low-carbohydrate eating pattern. They may use it as a short-term strategy to break through a weight loss plateau or enhance fat burning.  If you have specific medical conditions, such as epilepsy or metabolic disorders, a fat fast may be used as part of a therapeutic protocol under the guidance of health professionals experienced in managing these conditions.

Who Should Avoid a Fat Fast

Individuals with certain medical conditions, such as gallbladder disease, pancreatitis, or liver disorders and heart disease may face potential complications or exacerbation of symptoms when consuming too much fat in their diet. It’s important to consult with your health professional before attempting a fat fast if you have any underlying health conditions.

Strict dietary restrictions and extreme approaches like a fat fast can sometimes lead to an unhealthy relationship with food, disordered eating patterns, insufficient food intake, or feelings of deprivation and guilt. 


Remember that a fat fast is a short-term strategy and not suitable for everyone. Studies specifically addressing the long-term safety and effectiveness of fat fasting do not exist. It’s important to listen to your body and consult with a healthcare professional or registered dietitian to ensure you’re following a nutritionally balanced approach that meets your individual needs.

Katya Meyers, RD
Posted in Health & Science

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