The issue of how much protein to eat has been a major topic of conversation and some controversy in functional medicine circles over the past couple of years. The controversy has stemmed from a larger conversation and focus in the functional medicine community on the science of longevity. There is a large body of evidence, mostly from cell studies and animal research, along with some observational human studies, demonstrating that turning down the volume on certain cell growth signaling pathways (which include growth hormone, insulin, and insulin-like growth factor-1, among others) results in anti-aging and anti-cancer benefits¹. These growth pathways are stimulated by protein consumption, and– even more specifically–certain amino acids contained in proteins (methionine in particular) have been implicated. Indeed, restriction of methionine has been demonstrated in rats to improve metabolic flexibility (the ability to derive energy from a variety of substances) and increase energy expenditure, thereby limiting fat deposition, even without calorie restriction². (However, keep in mind that the applicability of rat studies to humans is a matter of debate, and the majority of the human evidence in this field is based on observational and cells/tissue studies.)
On the other hand, low protein consumption–especially in older adults–can set the stage for sarcopenia, a serious age-related muscle wasting condition which is an under-appreciated cause of disability and preventable death, in this country and elsewhere³. Additionally, muscle is recognized as a vital organ of glucose regulation and overall metabolic health. This is partly because muscle contractions stimulate glucose (read: sugar) uptake via an insulin-independent mechanism. (By the way, this is why walking or otherwise moving after eating is good for you!). Those advocating for higher protein diets maintain that muscle is the “organ of longevity,” and they cite research that higher protein diets have been shown to benefit both body composition⁴ and bone density⁵.
So, what gives? Well, I think that both sides to the protein debate do agree that as we age, our bodies need more protein to hang on to muscle and avoid frailty. There are, as you can imagine, different stances on what that amount of protein is, and like everything, there is going to be variation in individual need. My general rule of thumb for middle-aged adults that is supported by the research is 1.2-1.6 grams per kilogram (g/kg) of body weight per day. (Note that this is quite a bit higher than the RDA of 0.8 g/kg). To calculate this range for yourself, take your weight in pounds and divide by 2.2 to convert it to kilograms. Then, multiply this number by 1.2 to get your low-end value and by 1.6 to get your high-end value. For a 150-pound person, 1.2-1.6 g/kg is equal to 82-109 grams of protein per day. Also remember that it is mostly animal protein that is implicated as being pro-aging in human observational studies, so if plant protein feels good to your gut and your body, replacing some of your animal protein with plant protein could be a part of your longevity strategy⁶.
But also, I think an under-rated variable in the equation here is timing. As we age, when we eat our protein is as important as the quantity and quality of that protein if we want to optimize our bodies’ use of those amino acids. Here are my top three tips for timing protein intake:
- Check your serving size at each meal
Research shows that it is better for muscle maintenance to eat solid amounts of protein in single sittings rather than have smaller sprinklings throughout the day (remember that ill-advised “small meal” trend that was supposed to “boost” your metabolism?). Eating 2-3 meals with between 25 and 40 grams of protein in each meal (depending on your body size and goals) is preferable to eating snacks of 10 or so grams of protein smattered throughout the day. A 2015 study found that in a group of healthy men with an average age of 71, a meal containing 0.4 gram of protein per kilogram of body weight maximally stimulated muscle protein synthesis⁷. (In comparison, that number for the group of younger men in the study was 0.24 g/kg body weight). Not only will a larger amount of protein in each of 2-3 meals turn on muscle protein synthesis, but giving your digestive system time to work in between meals helps keep the gastrointestinal tract moving and aids digestion and assimilation of food. 0.4 g/kg in one meal translates to 1.2 g/kg for the whole day, assuming 3 meals. This is in line with the general guidance for muscle maintenance in older adults.
2. Don’t stack your protein at the end of the day
This is an extension of spacing throughout the day, but I think it warrants emphasis because with our daily schedules, the tendency is to have our largest meal at the end of the day, and this also means we are commonly eating our largest bolus of protein at the end of the day, which may not be the best choice for our metabolism or our muscle. We can still have a relaxing evening meal while more evenly spacing our protein consumption among 3 meals. One simple way to help yourself do this is to prepare extra protein at dinner and set aside a portion for breakfast or lunch the next day. If you struggle with eating protein earlier in the day, try eating 30 grams of protein at your breakfast meal and see how this affects your energy and cravings for the day. Whatever you do, don’t wait until dinner to feed yourself with a good amount of protein!
3. Eat protein after exercise
While protein is particularly important after resistance exercise, our muscles need refueling with a combination of protein and carbohydrate after any kind of workout. As we age, our muscles are less responsive to the anabolic (i.e., muscle-building) effects of amino acids, so it’s really important to get a good serving of high quality protein (i.e., containing all essential amino acids) in that first meal after exercising, whatever time of day that may be. Examples of high quality proteins include: whey protein powder*, eggs, meat, fish, dairy, soy, and hemp. Be mindful that the density of branched-chain amino acids that fuel muscle synthesis tends to be much lower in plant proteins (including soy) compared to animal proteins, and we need branched chain amino acids, especially leucine, to stimulate muscle cells growth and repair. A general rule of thumb is 2.5 grams of leucine in the post-workout meal. So if you are eating exclusively plant proteins, you will likely need to increase the amount of protein you are consuming. For example, there are roughly 2.5 grams of leucine in 25 grams of whey, but only half as much in 25 grams of soy protein. Pay attention to how your body responds to different proteins. Personal experimentation is key to finding what works for you in the long run.
*preferably grass-fed and without artificial/non-nutritive sweeteners and additives; I like Puori brand personally, but there are many options available
References
- Kitada, M., Ogura, Y., Monno, I., & Koya, D. (2019). The impact of dietary protein intake on longevity and metabolic health. EBioMedicine, 43, 632–640. https://doi.org/10.1016/j.ebiom.2019.04.005 https://pubmed.ncbi.nlm.nih.gov/30975545/
- Hasek, B. E., Stewart, L. K., Henagan, T. M., Boudreau, A., Lenard, N. R., Black, C., Shin, J., Huypens, P., Malloy, V. L., Plaisance, E. P., Krajcik, R. A., Orentreich, N., & Gettys, T. W. (2010). Dietary methionine restriction enhances metabolic flexibility and increases uncoupled respiration in both fed and fasted states. American journal of physiology. Regulatory, integrative and comparative physiology, 299(3), R728–R739. https://doi.org/10.1152/ajpregu.00837.2009 https://pubmed.ncbi.nlm.nih.gov/20538896/
- Cruz-Jentoft, A. J., Bahat, G., Bauer, J., Boirie, Y., Bruyère, O., Cederholm, T., Cooper, C., Landi, F., Rolland, Y., Sayer, A. A., Schneider, S. M., Sieber, C. C., Topinkova, E., Vandewoude, M., Visser, M., Zamboni, M., & Writing Group for the European Working Group on Sarcopenia in Older People 2 (EWGSOP2), and the Extended Group for EWGSOP2 (2019). Sarcopenia: revised European consensus on definition and diagnosis. Age and ageing, 48(1), 16–31. https://doi.org/10.1093/ageing/afy169 https://pubmed.ncbi.nlm.nih.gov/30312372/
- Kim, J. E., O’Connor, L. E., Sands, L. P., Slebodnik, M. B., & Campbell, W. W. (2016). Effects of dietary protein intake on body composition changes after weight loss in older adults: a systematic review and meta-analysis. Nutrition reviews, 74(3), 210–224. https://doi.org/10.1093/nutrit/nuv065 https://pubmed.ncbi.nlm.nih.gov/26883880/
- Lee, C. L., & Tsai, S. F. (2020). The impact of protein diet on bone density in people with/without chronic kidney disease: An analysis of the National Health and Nutrition Examination Survey database. Clinical nutrition (Edinburgh, Scotland), 39(11), 3497–3503. https://doi.org/10.1016/j.clnu.2020.03.014 https://pubmed.ncbi.nlm.nih.gov/32249111/
- Song, M., Fung, T. T., Hu, F. B., Willett, W. C., Longo, V. D., Chan, A. T., & Giovannucci, E. L. (2016). Association of Animal and Plant Protein Intake With All-Cause and Cause-Specific Mortality. JAMA internal medicine, 176(10), 1453–1463. https://doi.org/10.1001/jamainternmed.2016.4182 https://pubmed.ncbi.nlm.nih.gov/27479196/
- Moore, D. R., Churchward-Venne, T. A., Witard, O., Breen, L., Burd, N. A., Tipton, K. D., & Phillips, S. M. (2015). Protein ingestion to stimulate myofibrillar protein synthesis requires greater relative protein intakes in healthy older versus younger men. The journals of gerontology. Series A, Biological sciences and medical sciences, 70(1), 57–62. https://doi.org/10.1093/gerona/glu103 https://pubmed.ncbi.nlm.nih.gov/25056502/