The idea that there is a specific food that acts as the “off switch” for appetite is very compelling. Who hasn’t eaten more food than they planned or wanted? Whether it was too much of the same food or too much of a variety of foods, we often eat until we are stuffed. Wouldn’t it be amazing if we could eat something that could satisfy that drive to eat? According to Dr. Stephen Simpson and Dr. David Raubenheimer, that “something” is protein.
In their 2005 paper published in Obesity Reviews, Simpson and Raubenheimer proposed that obesity isn’t primarily caused by eating too much fat, or eating too many ‘carbs’, but by eating food that has too little protein [1]. They called this the “Protein Leverage Hypothesis”. This states is that humans have a built-in appetite for protein that drives food consumption. When we eat food that contains low an amount, we will over-eat until the amount we need is met.
In paleolithic times, the human diet was ~35% animal protein, 33% fat and the remainder plant material (which was limited in the diet due to antinutrients such as phytates, oxalates, tannins, trypsin-, amylase-, and protease inhibitors, and glycosides) [2]. Humans evolved and thrived eating this way.
In contrast, currently the percentage of protein in diets around the world remains at ~16% of daily calories [3] and Simpson and Raubenheimer believe that it is this ‘protein dilution’ of the diet that results in us overeating food, to try and obtain sufficient amounts.
In their 2005 paper, they wrote;
”The obesity epidemic is among the greatest public health challenges facing the modern world. Regarding dietary causes most emphasis has been on changing patterns of fat and carbohydrate consumption. In contrast the role of protein has largely been ignored because (i) it typically comprises only approximately 15% of dietary energy and (ii) protein intake has remained near constant within and across populations throughout the development of the obesity epidemic. We show that paradoxically these are precisely the two conditions that potentially provide protein with the leverage both to drive the obesity epidemic through its effects on food intake and perhaps to assuage it. [1]”
What this implies is, if we don’t intentionally prioritize protein in the diet, we will overeat fat and carbohydrate to reach the amount we require (or have evolved to eat).
To complicate matters, the food environment is made up of ultra processed foods that are mostly carbohydrate and fat. Snack and convenience foods were only introduced the early 1970s — which, coincidently was when the obesity epidemic began.
We have known since 2018 that foods high in both carbohydrate and fat result in more dopamine being released from the reward-center in striatum of our brain, than foods with carbohydrate alone, or fat alone [4]. This is why will often overeat French fries, but rarely a baked potato. Perhaps, the fact that snack and convenience foods are so low in protein is a contributing factor to us overeating them.
Current statistics indicate that 55% of calories eaten by adults [5] and 67% of calories eaten by children and teenagers [6] come from ultra-processed foods — high in both carbohydrate and fat, and low in protein.
A 2018 follow-up paper by Simpson and Raubenheimer based on the 2009-2010 National Health and Nutrition Examination Survey (NHANES) found higher consumption of ultra-processed foods was associated with lower protein density [7].
“Consistent with the Protein Leverage Hypothesis, increase in the dietary contribution of ultra processed foods was also associated with a rise in total energy intake, while absolute protein intake remained relatively constant [7].
“The protein-diluting effect of ultra processed foods might be one mechanism accounting for their association with excess energy intake [7].”
Rather than going in circles arguing whether eating too much fat or eating too many carbs resulted in obesity, perhaps it is more productive to focus on ensuring sufficient intake of high quality protein.
But how much is best? It depends for whom.
The Recommended Daily Allowance (RDA) for any nutrient is the average daily dietary intake level that is sufficient to meet the needs of 97-98 % of healthy people. The RDA is not the optimal requirement, but the absolute minimum to prevent deficiency.
The RDA – enough protein to prevent deficiency
The RDA for healthy adults is calculated at 0.8 g protein / kg of body weight [8]. A sedentary 70 kg / 154 pound man needs a minimum of 56 g and a sedentary 60 kg / 132 pound woman needs a minimum of 48 g protein per day.
Protein Needs for Active Healthy Adults
For physically active adults, the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine [9] recommend an intake of 1.2—2.0 g protein / kg per day to optimize recovery from training, and to promote the growth and maintenance of lean body mass.
Protein Needs for Older Adults
Several position statements by groups working with an aging population indicate that intake between 1.0 and 1.5 g protein / kg per day may best meet the needs of adults during aging [10, 11].
For the average, healthy 70 kg / 154 pound sedentary man this would be daily protein intake of 70 -105 g per day and for the average, healthy 60 kg / 132 pound sedentary woman this would be an intake of 60-90 g protein per day.
Range of Safe Intake
As written about in an earlier article, according to Dr. Donald Layman, PhD, Professor Emeritus, of Nutrition from the University of Illinois, the highest end of the range of safe intake of protein is 2.5 g protein/ kg per day.
For the average 70 kg / 154 pound sedentary man this would be a maximum daily protein intake of 175 g per day and for the average 60 kg / 132 pound sedentary woman, this would be a maximum protein intake of 150 g/ day.
Final Thoughts…
We know that the presence of both carbs and fat together in a food has a supra-additive effect on the pleasure center of our brain [4]. This leads to us eating way more of these foods, than foods with just carbs or just fat. Given this, it would make sense to avoid foods that have high amounts of both carbs and fat which include almost all of our favourite snack and convenience foods.
With the exception of nuts, seeds and milk most real, whole food is high in either carbs or fat, not both. Aim to eat these foods the most, but not together at the same meal.
Based on the Protein Leverage Hypothesis, aim to eat sufficient high protein foods based on your individual needs. Reach for foods such as salmon, tuna, skinless chicken and shrimp the most often. These contain 8 grams of protein per ounce (28 g) and 1.5 grams of fat. Enjoy a good ribeye, some pork or chicken legs that have on average 6.2 grams of protein per ounce (28g), and 6g of fat.
Vegetarian? No problem!
Cottage cheese has 28 g of highly bioavailable protein per cup, and Greek yogurt has 16 grams of protein per cup. Tofu only has ~4.7 grams of protein per ounce (28g), and is a complete protein containing all the essential amino acids.
Think of protein as a control button for appetite and reach for the types of protein that suit your lifestyle best!
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Joy
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References
- Simpson SJ, Raubenheimer D. Obesity: the protein leverage hypothesis. Obes Rev. 2005 May;6(2):133-42. doi: 10.1111/j.1467-789X.2005.00178.x. PMID: 15836464.
- Ben-Dor M, Gopher A, Hershkovitz I, Barkai R (2011) Man the Fat Hunter: The Demise of Homo erectus and the Emergence of a New Hominin Lineage in the Middle Pleistocene (ca. 400 kyr) Levant. PLoS ONE 6(12): e28689. https://doi.org/10.1371/journal.pone.0028689
- Lieberman HR, F.V., Agarwal S, et al. , Protein intake is more stable than carbohydrate or fat intake across various US demographic groups and international populations. The American Journal of Clinical Nutrition, 2020. 112(1): p. 180-186.
- DiFeliceantonio AG, Coppin G, Rigoux L, et al., Supra-Additive Effects of Combining Fat and Carbohydrate on Food Reward. Cell Metab. 2018 Jul 3;28(1):33-44.e3. doi: 10.1016/j.cmet.2018.05.018. Epub 2018 Jun 14. PMID: 29909968.
- Zefeng Zhang, Sandra L Jackson, Euridice Martinez, Cathleen Gillespie, Quanhe Yang, Association between ultraprocessed food intake and cardiovascular health in US adults: a cross-sectional analysis of the NHANES 2011—2016, The American Journal of Clinical Nutrition, Volume 113, Issue 2, February 2021, Pages 428—436, https://doi.org/10.1093/ajcn/nqaa276
- Lu Wang, Euridice Martínez Steele, Mengxi Du, Jennifer L. Pomeranz, Lauren E. O’Connor, Kirsten A. Herrick, Hanqi Luo, Xuehong Zhang, Dariush Mozaffarian, Fang Fang Zhang. Trends in Consumption of Ultraprocessed Foods Among US Youths Aged 2-19 Years, 1999-2018. JAMA, 2021; 326 (6): 519 DOI: 10.1001/jama.2021.10238
- Martínez Steele E, Raubenheimer D, Simpson SJ, Baraldi LG, Monteiro CA. Ultra-processed foods, protein leverage and energy intake in the USA. Public Health Nutr. 2018 Jan;21(1):114-124. doi: 10.1017/S1368980017001574. Epub 2017 Oct 16. PMID: 29032787.
- National Academies Press, Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein and Amino Acids (2005)
- Thomas DT, Erdman KA, Burke LM. American College of Sports Medicine Joint Position Statement. Nutrition and Athletic Performance [published correction appears in Med Sci Sports Exerc. 2017 Jan;49(1):222]. Med Sci Sports Exerc. 2016;48(3):543-568. doi:10.1249/MSS.0000000000000852
- Fielding RA, Vellas B, Evans WJ, Bhasin S, et al, Sarcopenia: an undiagnosed condition in older adults. Current consensus definition: prevalence, etiology, and consequences. International working group on sarcopenia. J Am Med Dir Assoc. 2011 May;12(4):249-56
- Bauer J1, Biolo G, Cederholm T, Cesari M, et al. Evidence-based recommendations for optimal dietary protein intake in older people: a position paper from the PROT-AGE Study Group. J Am Med Dir Assoc. 2013 Aug;14(8):542-59
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