SUMMARY OF DOES PROTEIN SUPPRESS HUNGER AND THE PROTEIN LEVERAGE HYPOTHESIS
- Protein is associated with reduced hunger, but does protein suppress hunger if you already consume a high-protein diet? The protein leverage hypothesis proposes that protein dilution (i.e., low protein) in modern food supplies has led to increased energy intake through protein leverage.
- Calorie intake increases with declining protein concentrations in the diet, indicating a breakpoint at protein concentrations below physiological requirements.
- Adequate human protein intake threshold is set at just under 10%. Delving into the findings from randomized controlled trials (RCTs), it’s evident that protein leverage manifests within a protein range of 10% to 30%. Notably, a protein level of 5% is identified as falling beneath this critical breakpoint.
- In one study, researchers assigned subjects to a moderate (1.8 g/kg/day or .8 grams per pound) or a high protein diet (2.9 g/kg/day or 1.3 grams per pound of body weight) in conjunction with a 20% caloric restriction. Afterward, they could freely consume carbs and fats, but their protein intake remained constant. The moderate and high protein groups had similar appetite scores, indicating that increasing protein intake beyond a certain point doesn’t further suppress appetite.
- According to research studies, more protein will not lead to a reduction in appetite. However, protein overconsumption does not lead to weight gain or fat gain.
Introduction: Does protein help curb hunger
For many reasons, the Naked and Afraid TV series on the Discovery Channel is one of my favorite series to watch. If you have never seen the series, they take survivalists and drop them off with one other person in some remote location naked with no food or water. Survivors must find food and water, build a fire and shelter, and fight off wild animals and insects. It’s common for the participants to lose between 10 to 30 pounds while scavenging for food.
After a few days of no food, the survivalists always desperately search for one thing: protein! Interestingly, when starved, people look for protein above all macronutrients (i.e., carbohydrates or fat). You always hear them say, “I need protein; I can feel my body breaking down!” The series emphasizes two crucial aspects of protein intake. #1) You will lose a ton of muscle and fat in a calorie and protein-deficient state. #2 Appetite is ravenous in a protein-deficient state. One question that often arises is, does protein suppress hunger? The series provides some anecdotal evidence in this regard.
In this month’s issue of Body by Science by Dr. Campbell, there was a great issue with protein intake and appetite regulation. As I read the issue, I considered the similarities between Naked and Afraid participants in a protein-deficient state and what the researchers found in several studies when protein was deliberately reduced. The question of does protein suppress hunger was at the forefront of my mind. No, the research subjects did not have to run around naked and find wild animals to kill, but I wanted to highlight some of the critical points of protein restriction studies and appetite regulation. But also, does protein reduce hunger in a significant way?.
Obesity and Protein: Does protein reduce hunger
Over the past six decades, the surge in obesity rates among humans has become a significant health concern. One of the primary culprits behind this trend is excess energy intake, especially from fats and carbohydrates. (Speakman et al., 2023) These two macronutrients have been the dominant sources of the surplus calories consumed by various populations. Interestingly, while protein contributes to our daily caloric intake, it hasn’t been the direct cause of the global obesity epidemic.(Lieberman et al., 2020) But does protein suppress hunger and thereby reduce calorie intake? The research is still ongoing, but prioritizing protein at meals and snacks is a good idea for many reasons. And does protein help curb hunger in the long run?
PROTEIN INTAKE AND APPETITE
Protein is a crucial component of our diet, serving functions beyond muscle building. It’s vital for repairing tissues, producing enzymes, and synthesizing hormones, among other roles. Many species, including humans, exhibit a behavior termed “protein prioritization.” These species tend to favor protein consumption over other nutrients when presented with a choice. This behavior underscores the importance of protein sources in our dietary choices and overall health.(Raubenheimer & Simpson, 2023)
Many popular food options are processed snacks and dinners high in carbohydrates and fats but low in protein. Consuming these low-protein foods may lead to a continuous cycle of hunger and eating, resulting in excess calorie consumption to meet protein needs. Many studies have found that low-protein foods can lead to an increase in extra calories. (Lejeune et al., 2005) Studies have found a correlation between lower family incomes and diets lower in protein and higher in carbohydrates, which may explain the association between socioeconomic status and obesity incidence.(Raubenheimer & Simpson, 2023) So, does lean protein help curb hunger? Many studies suggest that it does. But also, does protein reduce hunger in a broader sense?
What is the Protein Leverage Hypothesis?
The Protein Leverage Hypothesis (PLH) is a theory that proposes that humans and other animals have a specific appetite for protein and that this appetite drives food intake and energy balance. (Simpson & Raubenheimer, 2005) Several studies have supported the PLH. For example, humans and animals prioritize protein over other macronutrients, such as fat and carbohydrates (Simpson & Raubenheimer, 2005).
In a study by Griffioen-Roose et al., participants underwent a randomized crossover experiment. Participants were first put on a low-protein diet (containing only 5% protein) for 14 days. After this pre-treatment phase, when given free choice from a broad selection of foods, these healthy adults preferred foods that were high in protein and had a savory flavor. This behavior led to an increase in their protein consumption. Interestingly, despite this shift in dietary preference, there was no change in their overall energy intake.
In essence, the study suggests that when people are on a low-protein diet, they naturally gravitate towards high-protein foods when given a choice, likely to compensate for the reduced protein intake during the pre-treatment phase. This leads us back to the question: does protein suppress hunger? The series provides some anecdotal evidence in this regard. But another question is, does protein help curb hunger? And does protein help curb hunger in various situations? The series hints at this as well.
IS LOW PROTEIN CONTRIBUTING TO THE OBESITY EPIDEMIC?
According to the PLH, when the proportion of protein in the diet is low, individuals will consume more food to meet their protein needs, leading to excess energy intake and potential weight gain. (Simpson & Raubenheimer, 2005) This hypothesis suggests that the rise in obesity rates may be partially attributed to a shift towards diets with reduced protein density relative to the set point for protein regulation and body fat. (Raubenheimer et al., 2014) One study found evidence to support the protein leverage hypothesis by showing that individuals underrate relative to calorie balance from diets containing a higher protein-to-carbohydrate + fat ratio. This suggests a higher protein intake may reduce calorie intake and help suppress appetite.
The Science Behind Protein Leverage:
The PLH also suggests that how much protein you consume can influence how many calories you consume. (Raubenheimer & Simpson, 2016) It has been proposed that humans have a relatively strong appetite for protein-rich foods (i.e., how much protein and EAAs are consumed). If insufficient protein is consumed, overconsumption of calories occurs (Raubenheimer & Simpson, 2016). This means that when protein-rich foods are available, individuals may consume more calories to meet their protein needs. Protein-specific cravings will stimulate the drive for increased food intake when the amount of protein in the diet is limited. (Leidy et al., 2015) However, not all scientists agree with the PLH. The debate on whether protein suppresses hunger continues. And does protein reduce hunger in the broader context of consuming enough protein?
PLH IS NOT UNIVERSALLY ACCEPTED AS THE CAUSE OF OBESITY
Some researchers have questioned how much protein leverage influences energy intake and weight regulation. Kevin Hall, a world-renowned obesity expert, suggests that despite consistent protein intake over the past decade, obesity has risen. (Hall, 2018) This highlights the need for further research to fully understand the role of protein leverage in different populations and contexts, including its impact on weight management.
DOES PROTEIN SUPPRESS HUNGER STUDY
A 2011 study measured different dosages of protein and its effect on appetite suppression. The great aspect of this study was that it was conducted in a clinical research setting, so the subjects had to stay in the research center, and they measured all the food they consumed. The researchers measured calories consumed and feelings of hunger. The subjects completed 4 days of various levels of protein.
- Low Protein: 10% Protein, 60% carbohydrates, 30% Fat
- Moderate Protein: 15% protein, 55% carbohydrates, 30% Fat
- High Protein: 25% protein, 45% carbohydrates, 30% Fat
The participants were allowed to eat as much food as they wanted (i.e., as little or as much as they wished to). The subjects were allowed to walk an hour a day at the research center, but they controlled the exercise so that all the subjects burned the same number of calories from exercise.
The results were clear: those on the low protein (10% protein diet) ate about 260 more calories daily. Those who consumed low protein also were hungrier. However, there was no difference in the number of calories consumed in the moderate and high protein diets (i.e.,15-25% protein). This suggests that a certain amount of protein is needed, but consuming more protein, up to 30%, may result in fewer calories consumed and better appetite suppression.
How Much Protein is Optimal
Research suggests that although it’s not harmful to consume more protein and does not contribute to kidney disease in healthy patients, the appetite-suppressing effects of protein seem to stop after intakes above 1.8 g/kg/day (the amount of protein equal to .8 grams per pound of bodyweight). In one study, researchers assigned subjects to a moderate (1.8 g/kg/day or .8 grams per pound) or a high protein diet (2.9 g/kg/day or 1.3 grams per pound of body weight) in conjunction with a 20% caloric restriction.
Afterward, they could freely consume carbs and fats, but their protein intake remained constant. The moderate and high protein groups had similar appetite scores, indicating that increasing protein intake beyond a certain point doesn’t further suppress appetite.
The high protein group did not result in less hunger in resistance-trained individuals during short-term calorie-restricted diets. The appetite-regulating hormones ghrelin and PYY responses were maintained following moderate protein diets. However, athletes experiencing negative symptoms (i.e., hunger cravings) may benefit from protein-rich meals instead of overconsumption of protein.
Furthermore, a 2020 study found that protein reduces appetite by lowering the hunger hormone ghrelin and increasing satiety hormones CCK and GLP-1. High-protein diets did not show any long-term hunger-reducing effects. Many athletes consume excessive protein for its appetite-suppressing results, potentially neglecting other beneficial macronutrients.(Kohanmoo et al., 2020)
The practical applications of the protein leverage hypothesis for people dieting are that increasing dietary protein intake may help to reduce overeating and promote weight loss, as well as preserve and build muscle mass. This is because protein is more satiating than fat or carbohydrates and helps regulate appetite and energy intake. Therefore, individuals trying to lose weight may benefit from increasing their protein intake while reducing their intake of high-fat and high-carbohydrate foods.
So, does protein reduce hunger? According to the research, increasing protein intake from 15% to 25% did not decrease energy intake. However, there was a greater increase in hunger score between 1 and 2 hours after the 10% protein breakfast compared to the 25% protein breakfast, suggesting that increasing protein intake may have a greater suppression effect on appetite than less protein intake. Furthermore, protein overconsumption will not result in weight gain.
Hall, K. D. (2018). Did the Food Environment Cause the Obesity Epidemic? Obesity (Silver Spring), 26(1), 11-13. https://doi.org/10.1002/oby.22073
Kohanmoo, A., Faghih, S., & Akhlaghi, M. (2020). Effect of short- and long-term protein consumption on appetite and appetite-regulating gastrointestinal hormones, a systematic review and meta-analysis of randomized controlled trials. Physiol Behav, 226, 113123. https://doi.org/10.1016/j.physbeh.2020.113123
Leidy, H. J., Clifton, P., Astrup, A., Wycherley, T. P., Westerterp-Plantenga, M. S., Luscombe-Marsh, N. D., Woods, S. C., & Mattes, R. D. (2015). The Role of Protein in Weight Loss and Maintenance. American Journal of Clinical Nutrition. https://doi.org/10.3945/ajcn.114.084038
Lejeune, M. P. G. M., Kovács, É., & Westerterp-Plantenga, M. S. (2005). Additional Protein Intake Limits Weight Regain After Weight Loss in Humans. British Journal of Nutrition. https://doi.org/10.1079/bjn20041305
Lieberman, H. R., Fulgoni, V. L., Agarwal, S., Pasiakos, S. M., & Berryman, C. E. (2020). Protein intake is more stable than carbohydrate or fat intake across various US demographic groups and international populations. Am J Clin Nutr, 112(1), 180-186. https://doi.org/10.1093/ajcn/nqaa044
Raubenheimer, D., Machovsky‐Capuska, G. E., Gosby, A. K., & Simpson, S. J. (2014). Nutritional Ecology of Obesity: From Humans to Companion Animals. British Journal of Nutrition. https://doi.org/10.1017/s0007114514002323
Raubenheimer, D., & Simpson, S. J. (2016). Nutritional Ecology and Human Health. Annual Review of Nutrition. https://doi.org/10.1146/annurev-nutr-071715-051118
Raubenheimer, D., & Simpson, S. J. (2023). Protein appetite as an integrator in the obesity system: the protein leverage hypothesis. Philos Trans R Soc Lond B Biol Sci, 378(1888), 20220212. https://doi.org/10.1098/rstb.2022.0212
Simpson, S. J., & Raubenheimer, D. (2005). Obesity: The Protein Leverage Hypothesis. Obesity Reviews. https://doi.org/10.1111/j.1467-789x.2005.00178.x
Speakman, J. R., de Jong, J. M. A., Sinha, S., Westerterp, K. R., Yamada, Y., Sagayama, H., Ainslie, P. N., Anderson, L. J., Arab, L., Bedu-Addo, K., Blanc, S., Bonomi, A. G., Bovet, P., Brage, S., Buchowski, M. S., Butte, N. F., Camps, S., Cooper, J. A., Cooper, R., . . . Wong, W. W. (2023). Total daily energy expenditure has declined over the past three decades due to declining basal expenditure, not reduced activity expenditure. Nat Metab, 5(4), 579-588. https://doi.org/10.1038/s42255-023-00782-2
Does Protein Suppress Hunger like many assume it does? The Protein Leverage Hypothesis posits a powerful effect of protein on appetite regulation. Numerous studies have shown that a high protein intake, often sourced from whey protein powder, can lead to a much higher thermic effect than other macronutrients, known as the thermic effect of food. This thermic effect boosts the metabolic rate, counteracting the metabolic slowdown often seen in calorie-restricted diets.
Consuming grams of protein through protein powder, especially whey protein, can prevent muscle loss during a calorie deficit, especially when combined with strength training. Older adults and overweight women can reap significant health benefits from a diet plan rich in protein, including stabilized blood sugar levels and a reduced risk of obesity. Yet, the most important factor remains the modest increase in peptide yy, a hormone that signals satiety, after consuming protein-rich meals.