If you don't have time to watch the excellent video above, here are some key points made by Dr. Layman:
- The Institute of Medicine's range for protein intake is very broad: 0.8-2.5 grams per kilogram of body weight per day, or 56-200 grams per day
- Always use absolute protein (grams) instead of percentage of calories from protein (15% of calories from protein would be only 45 grams on a 1200-calorie diet but 113 grams on a 3000-calorie diet)
- Study results don't all agree due to varying levels of compliance (Measures of compliance are often not reported)
- Distribution of protein throughout the day in at least 3 feedings is important. Less than 20 grams of protein per meal has no effect on protein synthesis, and 60 grams of protein in one sitting is more than your body can effectively use
- When oxidized, essential amino acids act as signaling molecules for metabolism, including tryptophan as a precursor for the synthesis of serotonin, phenylalanine's release of the satiety-promoting gut hormone CCK; and leucine for muscle protein synthesis (MPS).
There's plenty of research in favor of moderately high protein consumption, including a study Dr. Layman published earlier this year expanding on many of the concepts above, such as the amount and type of protein required at mealtimes to optimize leucine's effects on MPS: 3 grams of leucine per meal, or a minimum of ~25 grams of protein per meal (1).
Also, while insulin is viewed by many in the low-carb community as a "storage" hormone, it's actually an anabolic hormone that promotes growth in children and increased muscle mass in adults. Chronically high levels of fasting and postmeal insulin are indeed unhealthy, but along with leucine, a small rise in this hormone after meals is vital for MPS. Also, research suggests that much like insulin resistance, aging may produce "leucine resistance," which requires additional amino acids in order to promote MPS signaling (1).
Muscle protein breakdown (MPD) and MPS occur in everyone and should be in balance in order to maintain muscle mass. If your goal is to increase muscle size, the ratio of MPS to MPD must be increased through strength training as well as sufficient protein intake. Loss of lean muscle due to inadequate amino acid intake is one of the major drawbacks of fasting, which results in an extended period of (MPD), and "fat fasts," where a 1000-calorie, 90% fat diet is consumed for several days to break out of a weight loss plateau.
Weight loss: There's been much talk lately about striving for nutritional ketosis in order to lose weight. I've seen people encouraged to keep protein "moderate" (i.e., 1 gram per kilogram lean body mass) and increase fat intake in order to drive up serum ketone levels. But all the studies on low-carbohydrate diets supporting weight loss have used high protein intakes, whether ad libitum or prescribed (2-6), including the ones described as "very-low-carbohydrate ketogenic diets," whether urinary ketone levels were measured and reported or not. And for the record, I don't believe ketogenic diets promote weight loss any better than low-carbohydrate diets do and can in fact be counterproductive for weight loss at low protein and energy intakes.
Protein has the highest thermic effect of food (TEF) of the three macronutrients, meaning its digestion and absorption cause metabolic rate to increase significantly more than with carbohydrates or fat. An older study linked this effect to protein's high satiety value (7), and many studies have confirmed that with higher protein intake, people end up eating less as a result of feeling full and satisfied (8-10).
Retention of muscle mass: During weight loss, there's an inevitable loss of lean muscle tissue in addition to fat, regardless of diet and exercise. However, research has shown that increasing protein intake can minimize the amount of muscle lost during the process of losing weight (11). Higher protein intake can also decrease sarcopenia, or the loss of lean mass that occurs as a natural part of the aging process, estimated at 3-8% per decade after the age of 30 (12), and it's particularly effective when combined with resistance exercise. Dr. Bill Lagakos of Calories Proper wrote a great blog post demonstrating that nutritional ketosis in the absence of adequate protein (~100 grams per day for most) does not prevent a decline in muscle mass during weight loss. Bill has written many other excellent articles on protein and other topics, so please check out his blog if you haven't already.
Over the past few years, I've seen a disturbing trend in people who are trying to lose weight limiting protein to 50-60 grams per day in an attempt to achieve beta-hydroxybutyrate values over 1.5 mmol/L. (Fasting, of course, limits protein to zero grams for the duration of the fast). For therapeutic purposes such as epilepsy, brain cancer, neurological or mood disorders, this may be warranted. But I strongly disagree with this tactic for weight loss or diabetes management, the population group I primarily work with.
Protein is a satiating, self-limiting nutrient that increases metabolic rate, increases satiety, and helps maintain muscle health. So my question is why would we want to intentionally limit it if the goal is fat loss?
What about kidney health, bone health, and blood glucose levels?
There's a misconception that high protein intake is bad for the kidneys, but this seems to be based on the results of an older study on individuals who already had renal disease (13). Subsequent studies have demonstrated that high protein consumption (more than 1.5 grams per kg body weight) doesn't adversely affect the health of kidneys in people without preexisting renal disease (14). In fact, recent research suggests that even individuals with renal disease may not need to limit protein as previously believed, depending on the stage of disease. In 2013, researchers looked at the effect of a "moderate" protein diet (90-120 grams) vs. a "standard" protein diet (55-70 grams) in overweight and obese men with type 2 diabetes and impaired kidney function (15). This was a long-term study lasting two years, and in addition to weight loss and better blood glucose control, both groups saw an improvement in renal function.
I've written about the effects of high protein diets on bone health recently. It's a very long blog post, but if you skip to the "Protein" section at about the halfway point, you'll see that high-protein intake is actually beneficial rather than harmful for bone density, provided intake of minerals such as calcium are optimized and alkaline foods like vegetables are included in the diet.
And what about the effect of high protein intake on blood glucose levels in people with diabetes and prediabetes? Like the studies on weight loss discussed above, all of the carb0hydrate-restricted research verifying its benefits on glycemic control have been high in protein (often ad libitum amounts of meat, poultry, and eggs) (16-19), including one coauthored by Dr. Eric Westman in which 17 out of 21 subjects were able to eliminate or reduce dosage of insulin and/or oral diabetes medications over the course of the 16-week study(20). Although the amounts of food consumed weren't listed, most if not all of these participants were likely eating at least 100 grams of protein daily, given that their carbohydrate intake was less than 20 grams and portion sizes of protein foods weren't limited.
When the term "very-low-carbohydrate, ketogenic diet is used" in weight loss and diabetes research, it's referring to carbohydrate restriction -- not extremely high fat intake and definitely not protein restriction.
In 2004, Mary Gannon and Frank Nuttall studied 8 men with type 2 diabetes who followed a moderately low-carbohydrate (~100 grams net carbohydrate), high-fiber (~36 grams), very-high-protein (~200 grams) diet. After 5 weeks, fasting and postprandial blood glucose levels, insulin levels, and HbA1c had significantly improved (21). Of course, this was a very small study, but the results are pretty encouraging, given that dietary protein intake was roughly twice the amount consumed by most people.
Going with Science
When I say I'm in favor of high-protein, low-carbohydrate diets, I'm not recommending that most people eat anywhere close to the amount of protein consumed in the Gannon study. In fact, I don't think most of us could eat that much and feel well. Protein needs vary from person to person based on size, age, activity, and certain medical conditions. But I think we need to base low-carbohydrate recommendations on what the science shows, which is moderately high protein intake -- particularly during weight loss and aging -- on an ad libitum basis for most people.
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12. Arentson-Lantz E, et al. Protein: a nutrient in focus. Appl Physiol Nutr Metab.
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16. Nielsen JV, et al. Low-carbohydrate diet in type 2 diabetes: stable improvement of bodyweight and glycemic control during 44 months follow-up. Nutr Metab. 2006 Jun 14;3:22
17. Yamada Y, et al. A non-calorie-restricted low-carbohydrate diet is effective as an alternative therapy for patients with type 2 diabetes. Intern Med. 2014;53(1):13-9
18. Unwin D, Unwin J. Low carbohydrate diet to achieve weight loss and improve HbA1c in type 2 diabetes and pre-diabetes: experience from one general practice. Practical Diabetes 2014, 31: 76–79
19. Tay J, et al. Comparison of low- and high-carbohydrate diets for type 2 diabetes management: a randomized trial. Am J Clin Nutr. 2015 Jul 29pii: ajcn112581.[epub ahead of print]
20. Yancy WS, Westman EC, et al. A low-carbohydrate, ketogenic diet to treat type 2 diabetes. Nutr Metab. 2005 2:34
21. Gannon MC, Nuttall FQ: Effect of a high-protein, low-carbohydrate diet on blood glucose control in people with type 2 diabetes. Diabetes. 2004 53:2375–2382