Why am I gaining weight on an animal-based diet? Uncovering the Hidden Causes

December 9, 2025 •

5 min read

Despite the common belief that animal-based diets inherently cause weight loss, many individuals report gaining weight after adopting this eating style. This unexpected weight gain can be frustrating and confusing, but it often stems from several common, addressable factors beyond just the diet itself.

Quick Summary

Gaining weight on an animal-based diet can result from a calorie surplus, high fat intake, poor macro balance, or lifestyle factors like stress. Adjusting your food choices and habits can help address this issue.

Key Points

Calorie Surplus is Still Key: Gaining weight on an animal-based diet is usually caused by consuming more calories than you burn, often due to the high calorie density of fatty animal products.
Fat is Calorie-Dense: With 9 calories per gram, fat can quickly add up, so be mindful of portion sizes and the fattiness of your food choices like ribeye or added butter.
Excess Protein Adds Up: While protein is beneficial, excess consumption can be converted to glucose and stored as fat, contributing to a calorie surplus.
Consider Leaner Cuts: To reduce calorie intake, focus on leaner meats like chicken breast, fish, and sirloin, rather than only fatty cuts like brisket or pork belly.
Lifestyle Affects Weight: Factors like inadequate sleep, high stress, and lack of exercise can negatively impact weight loss by increasing cortisol and affecting metabolism.
Initial Water Weight Fluctuations are Normal: It's common to experience temporary weight gain due to water retention and metabolic shifts when starting a new restrictive diet like the carnivore diet.

The Calorie Surplus Equation

Many people assume that because an animal-based diet is satiating, they cannot overeat. However, the fundamental principle of weight management still applies: consuming more calories than you burn leads to weight gain. Animal products, especially fatty cuts of meat and dairy, are incredibly calorie-dense. A ribeye steak, for example, can contain hundreds of calories in a single serving. While protein and fat provide strong satiety signals, they do not make you immune to consuming too many calories if portion sizes are too large or meal frequency is excessive.

The High-Fat Pitfall

On many low-carb versions of an animal-based diet, fat becomes the primary fuel source. Fat contains 9 calories per gram, more than double the caloric density of protein and carbohydrates, which both contain 4 calories per gram. It is easy to accumulate a significant calorie surplus by regularly consuming fatty cuts of meat, adding extra butter or tallow, and including high-fat dairy like cheese and heavy cream. A seemingly small addition of cooking fat or a fattier meat choice can dramatically increase the total calorie count of a meal, moving you from a caloric deficit to a surplus without much change in volume.

Protein Overload and Gluconeogenesis

While protein is crucial for muscle repair and satiety, consuming excessive amounts can contribute to weight gain. The body can convert excess protein into glucose through a process called gluconeogenesis, which can then be stored as fat if not used for energy. Moreover, excess protein intake, particularly from animal sources, is still calorie intake. If you are consistently eating more protein than your body needs, it can tip the scales toward a calorie surplus, especially if combined with high fat intake. Finding the right protein-to-fat ratio is essential for managing your caloric intake on an animal-based plan.

Transition and Initial Adjustments

When you first switch to a restrictive diet like an animal-based or carnivore plan, your body undergoes significant metabolic shifts. It is common to experience initial weight fluctuations that are not necessarily fat gain. Water retention is a key factor here. Changes in electrolyte balance, particularly sodium and potassium, can cause your body to hold onto more water. Your digestive system also needs to adapt to the absence of fiber from plants, which can cause temporary constipation or bloating. These temporary shifts can register as weight gain on the scale and are often not a long-term issue.

Comparing Healthy vs. Unhealthy Low-Carb Approaches

Research has shown that not all low-carb diets are created equal. Diets that emphasize healthy, minimally processed animal products tend to have better outcomes than those relying heavily on processed meats and unhealthy fats. For example, a study comparing a healthy low-carb diet to an unhealthy one noted that participants consuming a diet high in processed meats gained more weight over time. This highlights the importance of food quality, even within the animal-based framework.

Comparison Table: Weight Gain Factors on Animal-Based Diets


Factor	Common Misconception	Reality on Animal-Based Diet
Caloric Intake	The diet is so satiating you can't overeat.	High calorie density of animal products makes it easy to exceed maintenance needs.
Fat Intake	Eating fat doesn't make you fat on keto/carnivore.	Fat contains more than twice the calories per gram of protein and carbs, leading to quick calorie accumulation.
Protein Intake	You can eat unlimited protein without consequence.	Excess protein can be converted to glucose and contribute to a calorie surplus if not needed for muscle repair.
Physical Activity	Diet alone is enough for weight loss.	Insufficient movement and exercise can prevent a caloric deficit, even with a restrictive diet.
Hidden Ingredients	Animal products are always clean.	Some processed animal products (e.g., sausages) contain added sugars and fillers that can cause weight gain.
Stress & Sleep	These external factors are unrelated to diet results.	High cortisol from stress and poor sleep can cause fat storage, especially around the midsection.

Actionable Steps to Address Weight Gain

If you find yourself gaining weight, it is time to reassess your approach. A few simple adjustments can make a significant difference.

Prioritize Leaner Protein: If weight loss is the goal, consider focusing on leaner protein sources. Choose options like chicken breast, fish (cod, salmon, trout), and leaner cuts of beef or pork. This helps reduce total fat and calorie intake while maintaining high protein levels for satiety.
Monitor Portion Sizes: Even without meticulous calorie counting, being mindful of portion sizes is crucial. Use smaller plates or simply reduce the amount of extra fat used in cooking to subtly decrease your overall intake.
Incorporate Physical Activity: Weight management is a two-part equation: diet and exercise. Add regular physical activity to your routine, such as walking, strength training, or cycling, to increase your calorie expenditure.
Evaluate Dairy and Processed Meats: If you include dairy, check if it's a high-calorie contributor. Processed meats like sausages or bacon can also contain additives or excess fat, so opting for whole, unprocessed animal products is always the better choice.
Manage Stress and Sleep: High cortisol levels from chronic stress can lead to increased fat storage. Prioritizing quality sleep and finding effective stress management techniques are vital for overall health and weight goals.

The Role of Individual Variance and Hormones

It's important to recognize that everybody responds differently to diet. Factors like genetics, insulin sensitivity, and hormonal health play a large role. Some individuals, especially those with pre-existing conditions like hypothyroidism or hormonal imbalances, may find weight loss more challenging even on a strict animal-based diet. If weight gain persists despite consistent efforts, consulting with a healthcare professional can help rule out underlying issues.

Conclusion

While an animal-based diet can be a powerful tool for health and weight management, it is not a magic bullet. Gaining weight is often the result of a calorie surplus, which is surprisingly easy to achieve with the diet's high-fat, high-calorie foods. By focusing on leaner cuts, controlling portion sizes, staying active, and managing lifestyle factors like stress and sleep, you can address the root cause of weight gain and get your progress back on track. Understanding the calorie density of animal products and listening to your body's signals are key to making this dietary approach work for you. For more information on dietary comparisons, the National Institutes of Health has published studies contrasting low-carb and low-fat diets.

Frequently Asked Questions

Yes, it is possible to gain weight on a carnivore or animal-based diet. Weight gain typically occurs when you are in a caloric surplus, which can easily happen with the high calorie density of fatty animal products, even though the diet is often satiating.

While fat is a key energy source on a low-carb diet, consuming too much fat, even from healthy sources like tallow or ghee, can lead to a caloric surplus and subsequent weight gain. Fat contains more calories per gram than protein or carbs, so portion control is important.

To lose weight on an animal-based diet, focus on consuming leaner protein sources, controlling portion sizes, and incorporating regular physical activity. Ensure you are not over-relying on high-fat dairy or overly fatty cuts of meat.

Physical activity is crucial for weight management on any diet. Exercise helps increase your total calorie expenditure, making it easier to achieve a caloric deficit. It also helps with muscle maintenance and hormone regulation.

Yes, some people experience initial weight fluctuations, including temporary weight gain, when transitioning to an animal-based diet. This can be due to changes in water retention and electrolyte balance as your body adjusts to the new way of eating.

High stress levels can lead to increased cortisol, a hormone that promotes fat storage, especially in the abdominal area. Managing stress through adequate sleep, relaxation, and other healthy coping strategies is important for preventing weight gain.

While strict calorie counting is not required for everyone, being mindful of your total intake is important, especially if weight loss is your goal. Using portion control and being aware of the calorie density of fatty animal products can help prevent a calorie surplus.