High protein diets and metabolism: Part 3
By Ari Snaevarsson, Features Editor
The TEF of protein
As we bring the physiology side of this series to an end, another factor worth considering is the relatively higher thermic effect of food (TEF) – which I went over in my article on meal frequency and weight loss – of protein.
Remember, this is the energy cost to digest, absorb, transport, store/use, and excrete nutrients. While the TEF of dietary fat rarely exceeds 10%, the TEF of protein lies somewhere in between 20 and 35% (Westerterp, 2004). This is because of the amount of processing that protein must undergo in the liver, as well as the fact that the protein synthesis it promotes requires a great deal of ATP – adenosine triphosphate, our body’s cellular energy currency (Bier, 1999).
According to the estimations of nutrition wizard Lyle McDonald – who I interviewed over on my site, NoFluffStrength – for every 100 calories’ worth of carbohydrates or fat you replace with 100 calories in protein, you would burn 25 more calories in the process of TEF.
That is to say, you would essentially only “store” 70% of the protein ingested (note: we do not have the capacity to store amino acids, but we can use this model conceptually), versus about 95% of carbohydrates or fat. There is much more to this story, as protein metabolism is a topic that would take an entire book to comprehensively cover – and, surely enough, Lyle has done just that in his book aptly named “The Protein Book.” So, if this interests you, check out both that book and the relevant articles over on my site.
Practicality of the TEF of protein in dieting
However, this only proves seriously consequential for dieting concerns when one is replacing a large proportion of fat or carbohydrates with protein. It is usually only within the context of a protein-sparing modified fast (PSMF) – an extreme measure in which the diet is composed almost entirely of protein – that this results in weight loss much beyond what would be predicted by caloric imbalance alone.
It should be noted this type of crash diet relies on other mechanisms, in addition to the increased TEF, to elicit greater fat loss (such as ketosis and purposeful gluconeogenesis from amino acid substrate) which was not only elucidated by McDonald’s work in The Protein Book but also by Sukkar et al. (2013) studying a tube-fed PSMF diet in obese type 2 diabetic patients.
I may delve into this in a later article, as I spent a good deal of my contest prep this past summer running a PSMF, but for now it suffices to say that under no conditions should this diet be executed until the dieter is fully educated on the biochemistry at play and what safety protocols should be employed (because, yes, people have died from running protein-only diets improperly).
Satiety and thermogenesis
At first glance, this may seem unrelated to our discussion on protein’s impact on metabolic rate, but there is actually much evidence, such as that by Westerterp-Platenga, Rolland, Wilson, & Westerterp (1999), to suggest that the well known satiating effect of protein is mediated through its dietary-induced thermogenesis (DIT).
That is to say, the greater amount of energy expended in metabolizing dietary protein works as a signal (through various signalling molecules and pathways) to slow down our drive to seek out more food, telling us we already have a sufficient bolus to digest and “store” as is.
Preservation of muscle mass
This is an area that it admittedly did not occur to me to include until this week. While I have now written, at some considerable length, about the interplay between protein intake and muscle mass, I have only so far spoken to the “high RMR of muscle” theory. What also deserves some mention is the implication behind the muscle mass growth or retention promoted by protein.
That is to say, paired with appropriately programmed resistance training, an adequate protein intake in the context of a caloric deficit will absolutely work to preserve muscle mass (Paddon-Jones et al., 2003).
So, when the body needs to look to some store of nutrients to rely on for energy, we can partition it away from catabolizing muscle (literally meaning to degrade amino acids into ketone bodies and then possibly glucose) for these needs.
This, in theory, would then lead to greater utilization of glycogen and fat stores (Layman et al., 2005). Indeed, in obese patients put on isocaloric high protein diets and resistance training programs, though total weight loss was not significantly different from control, more muscle mass preserved, and therefore proportionally more body fat lost (Verreijen et al., 2015).
Is protein-sparing a sincere concern?
Now, the severity of caloric restriction (CR) necessary to induce this “burning of muscle” for energy, and the magnitude to which this would take place, is probably not in accordance with the simplistic model referred to in typical nutrition guru sound bites. Though the available evidence is limited here (and CR protocols tend to be rather poorly executed), there is some concrete data out there.
Research author Forbes (2000) showed that the proportion of weight loss coming from one’s muscle mass will be greater in individuals who are lean from the onset of dieting. There is also reason to believe that a slower expectation for weekly weight loss can translate into more retention of muscle mass (Garthe, Raastad, Refsnes, Koivisto, & Sundgot-Borgen, 2011) Hopefully, I have made this issue slightly easier to conceptualize. It is imperative we not take reductionist aphorisms at face value but instead meet them with informed skepticism. The story is not as simple as “protein increases your metabolism” or even “more protein means more muscle mass, which has a higher metabolic rate.” Now that the physiology side of the series is over, in next week’s article, I can turn what we have learned into actionable advice you can follow, along with some more quick details about protein’s physiological effects in a diet.
- Forbes GB. Body fat content influences the body composition response to nutrition and exercise. Ann N Y Acad Sci 904: 359–365, 2000.
- Garthe I, Raastad T, Refsnes PE, Koivisto A, Sundgot-Borgen J. Effect of two different weight-loss rates on body composition and strength and power-related performance in elite athletes. Int J Sport Nutr Exerc Metab 21: 97–104, 2011.
- Layman DK, Evans E, Baum JI, Seyler J, Erickson DJ, Boileau RA. Dietary Protein and Exercise Have Additive Effects on Body Composition during Weight Loss in Adult Women. J Nutr 135: 1903–1910, 2005.
- Paddon-Jones D, Sheffield-Moore M, Zhang X-J, Volpi E, Wolf SE, Aarsland A, Ferrando AA, Wolfe RR. Amino acid ingestion improves muscle protein synthesis in the young and elderly. American Journal of Physiology – Endocrinology and Metabolism 286: E321–E328, 2004.
- Bier D. The Energy Costs of Protein Metabolism: Lean and Mean on Uncle Sam’s Team [Online]. National Academies Press (US).
- Sukkar SG, Signori A, Borrini C, Barisione G, Ivaldi C, Romeo C, Gradaschi R, Machello N, Nanetti E, Vaccaro AL. Feasibility of protein-sparing modified fast by tube (ProMoFasT) in obesity treatment: a phase II pilot trial on clinical safety and efficacy (appetite control, body composition, muscular strength, metabolic pattern, pulmonary function test). Med J Nutrition Metab 6: 165–176, 2013.
- Verreijen AM, Verlaan S, Engberink MF, Swinkels S, Bosch J de V den, Weijs PJ. A high whey protein–, leucine-, and vitamin D–enriched supplement preserves muscle mass during intentional weight loss in obese older adults: a double-blind randomized controlled trial. Am J Clin Nutr 101: 279–286, 2015.
- Westerterp KR. Diet induced thermogenesis. Nutr Metab (Lond) 1: 5, 2004.
- Westerterp-Plantenga MS, Rolland V, Wilson SAJ, Westerterp Kr. Satiety related to 24 h diet-induced thermogenesis during high protein/carbohydrate vs high fat diets measured in a respiration chamber. European journal of clinical nutrition 53: 495–502, 1999.