Does excess protein turn into fat
Pro Research Analysisby 
Searched over 200M research papers
Does Excess Protein Turn Into Fat?
Protein Metabolism and Energy Balance
Excess protein intake can influence the body's energy balance and metabolism. When protein is consumed in amounts exceeding the body's needs for muscle repair and other functions, it can be converted into glucose through a process called gluconeogenesis. This glucose can then be used for energy or stored as fat if it is not needed immediately 2. This conversion process is particularly relevant when energy demand is low, as the surplus protein contributes to a positive energy balance, potentially leading to fat accumulation 2.
Impact of High-Protein Diets on Weight and Fat Loss
High-protein diets are often promoted for weight loss due to their ability to increase satiety and reduce overall calorie intake. These diets can also enhance the thermic effect of food, which is the energy required to digest, absorb, and metabolize nutrients 2. However, while high-protein diets can be effective for weight loss, they may also pose risks if not balanced properly. For instance, excessive intake of branched-chain amino acids (BCAAs) in combination with a Western diet may exacerbate metabolic diseases 2.
Energy Expenditure and Protein Overfeeding
Studies have shown that overfeeding with protein increases energy expenditure more than overfeeding with fat. In a controlled trial, participants who consumed excess energy from protein showed a significant increase in 24-hour energy expenditure (24EE) and sleeping energy expenditure (SleepEE) compared to those who consumed excess energy from fat 3. This suggests that the body may handle excess protein differently, potentially reducing the likelihood of it being stored as fat compared to excess fat intake.
Protein and Fat Accumulation in the Liver
Excessive protein intake has also been linked to nonalcoholic fatty liver disease (NAFLD). High protein consumption, particularly in the context of an unhealthy Western diet, is associated with increased prevalence and severity of NAFLD. This is due to the altered plasma concentrations of amino acids, which contribute to intrahepatic fat accumulation 8. Therefore, while protein is essential for health, its excessive intake can have adverse effects on liver fat content and overall metabolic health.
Anabolic Sensitivity and Obesity
In overweight and obese individuals, the anabolic sensitivity of muscle protein synthesis to dietary protein is reduced. This means that despite consuming protein-dense foods, the muscle protein synthetic response is diminished compared to healthy-weight individuals 9. This impaired response may contribute to the difficulty in managing body composition and fat levels in obese populations.
Conclusion
In summary, while excess protein can be converted into fat under certain conditions, the body's response to protein overfeeding is complex and involves increased energy expenditure and potential metabolic benefits. However, excessive protein intake, especially in the context of a Western diet, can lead to adverse health outcomes such as NAFLD and metabolic diseases. Therefore, it is crucial to balance protein intake with overall dietary needs and energy expenditure to avoid negative health impacts.
Sources and full results
Most relevant research papers on this topic
Effect of acute and short-term dietary fat ingestion on postprandial skeletal muscle protein synthesis rates in middle-aged, overweight and obese men.
Acute and short-term dietary fat overload does not negatively impact skeletal muscle protein synthetic response to dietary protein ingestion in overweight/obese men, suggesting dietary-induced accumulation of intramuscular lipids is not associated with anabolic resistance.
RCTA high-protein diet for reducing body fat: mechanisms and possible caveats
High-protein diets may help reduce body fat through increased satiety hormones, reduced orexigenic hormone secretion, increased thermic effect of food, and improved glucose homeostasis, but may also exacerbate metabolic disease and pose a significant acid load to kidneys.
Rigorous Journal
Highly CitedEffect of protein overfeeding on energy expenditure measured in a metabolic chamber.
Excess energy from protein acutely stimulates 24-hour and SleepEE, while fat does not, with the strongest relationship being energy expenditure in tissue other than muscle or fat-free mass.
RCT
Very Rigorous JournalProtein-based Fat Replacers – A Review of Recent Advances
Protein-based fat replacers can effectively replace the majority of fat in food, with animal and plant-based options available, and their effects on food properties and nutritional value are reviewed.
Literature ReviewThe Diabetes Excess Weight Loss (DEWL) Trial: a randomised controlled trial of high-protein versus high-carbohydrate diets over 2 years in type 2 diabetes
Both low-fat high-protein and low-fat high-carbohydrate diets result in modest weight and waist circumference loss in overweight individuals with type 2 diabetes over 2 years.
RCT
Large Human TrialRigorous JournalHighly CitedProtein‐leverage in Mice: The Geometry of Macronutrient Balancing and Consequences for Fat Deposition
Mice regulate their intake of macronutrients, with protein intake prioritizing carbohydrates, and unbalanced foods low in protein lead to increased energy intake, which is converted into growth and storage.
Non-RCT
Animal StudyVery Rigorous JournalHighly CitedA word of caution against excessive protein intake
Excessive protein intake may have negative health consequences, while dietary protein is crucial for human health, but excessive consumption may lead to weight gain, muscle loss, and other issues.
Protein and amino acids in nonalcoholic fatty liver disease
High protein intake in unhealthy Western diets may contribute to nonalcoholic fatty liver disease, while increasing liver fat content during weight loss and maintenance.
Literature ReviewAnabolic sensitivity of postprandial muscle protein synthesis to the ingestion of a protein-dense food is reduced in overweight and obese young adults.
Overweight and obese adults have a diminished myofibrillar protein synthetic response to protein-dense food compared to healthy-weight controls.
Non-RCTVery Rigorous JournalHighly Cited