Are we pushing too much protein on midlife women?
Part 1 of my in-depth guide to meeting midlife protein needs
I’m scrolling my midlife insta feed and spot a before and after reel of a midlife woman. She’s lifting weights and is lean.
She says she got this way doing two things.
Heavy lifting and protein. She consumes one gram of protein for every pound she weighs, and she tailors her meals and snacks to build muscle.
These days, protein is all us midlife women seem to hear about. But is all this protein pushing helping or compromising health and well-being?
As a midlife dietitian, I also focus on strength training and protein, in addition to many other things. Yet, I'm observing a trend of excessive focus on protein and lifting as the ultimate keys to health.
So, let’s settle in and examine the evidence on protein and health outcomes for midlife women in part 1 of this in-depth guide.
Why protein anyway?
As we get older, not only is it more important to meet protein needs, but we’re also less likely to do so.
About 30% of 50-year-olds do not meet the recommended amount of protein which is .8g/kg body weight. And 10% of older women fail to meet the estimated average requirement of .66g.
Yet it’s important to remember that these recommendations are based on the minimum protein intake to balance the loss of nitrogen in the body. Most health professionals acknowledge that protein needs increase with age.
Anabolic resistance is a term used to describe the blunted effect of muscle protein synthesis (MPS) that occurs with aging. When MPS is less than muscle breakdown, we gradually lose skeletal muscle.
According to Don Laymen, professor Emeritus in the Department of Food Science and Human Nutrition at the University of Illinois at Urbana-Champaign, one key change is MPS switches from growth hormone driven to a leucine trigger after 30.
In short, young adults have an easier time maintaining and building muscle mass. But by the third decade, relative muscle mass and power begin to decline.
Studies reveal that the median loss of skeletal muscle per year after 40 is .37% which speeds up to .5% after 60, and .6-.7% after 75. Skeletal muscle makes up about half of lean body mass, and 30-40% of the body’s total mass.
However, adults who consistently exercise and consume enough protein usually don't experience declines until after 50.
The combination of exercise and protein ingestion has a positive, often synergistic effect on skeletal muscle protein synthesis. Recent analysis of NHANES data from Americans aged 50 y reinforces the synergistic relation between dietary protein intake, physical activity, and appendicular skeletal muscle mass.
- Paddon-Jones et al, Am J of Clin Nutr, 2015
What is a leucine trigger?
The amino acid leucine is important because it stimulates the mechanistic target of rapamycicn (mTOR) signaling, which increases MPS as a master regulator of cellular growth.
While <1g leucine is sufficient for young adults, studies indicate that >2.5g may be needed for MPS as we get older.
For instance, a study with 8,298 postmenopausal women found those in the highest category for both leucine intake and exercise had the highest adjusted lean mass across all BMI categories. When compared to the lowest intake for leucine, those in the highest had 12.6% higher lean body mass.
In a group of older adults, those who consumed >7.1g/day of leucine maintained their lean body mass over 6 years, while those with lower intake experienced lean body mass loss.
This is where animal protein has an advantage over plant protein. It not only contains all the essential amino acids, but it also contains more leucine. For instance, grains have about 6% leucine and whey has 12%. The average leucine intake in a typical mixed meal is about 8%, which is where the 30g protein recommendation per meal comes from (about 2.4g of leucine).
Although older persons appear to have a greater protein need, the requirement is, at least in part, driven by the increased need for the essential amino acid leucine.
-Phillips et al, Adv in Nutr, 2020
Maintaining lean body mass is a health issue
It’s clear that maintaining skeletal muscle is about more than looking lean, it’s a health issue.
First, skeletal muscle handles 75% of the disposal of glucose, making it the primary target organ for insulin‐dependent uptake of glucose.
Muscle also contains high levels of mitochondria, the energy powerhouse of cells. Mitochondria adapts to how active we are, which works to either increase or decrease energy production.
Muscle is the empowering leader of body composition, setting the tone for healthier fat and stronger bones with positive crosstalk from released cytokines.
With aging, low protein intake, and disuse of skeletal muscle, the crosstalk between muscle, fat and bone can turn sour. This leads to the release of proinflammatory cytokines, increasing bone breakdown, and increasing visceral fat.
Unfortunately, researchers mostly conduct studies on young and older adults. But we know that midlife is the ideal time to maximize lean mass before sarcopenia, loss of muscle mass and strength, sets in at older ages as stated in this 2015 review study:
Several lines of evidence support the concept that, similar to maximizing bone mass during peak accretion years, maximizing lean body mass before the onset of sarcopenia is feasible and likely useful in slowing its progression.
Along comes menopause
The changes with muscle and protein with aging are further affected by declining hormones during the menopause transition.
The removal of ovaries in mice cause a decline of satellite cells in muscle by 30-60%. These stem cells are key in helping muscle repair and regenerate.
When University of Minnesota researchers took biopsies in women before and after menopause, they discovered a link between satellite cells and levels of estrogen. Meaning as estrogen declined, so did satellite cells.
“This is the first work to show that estrogen deficiency affects the number as well as the function of satellite cells,” said co-senior author Dawn Lowe, PhD, in a press release.
Yet a 2019 meta-analysis on hormone therapy only showed a slight increase in muscle mass, which was nonsignificant. My guess is that hormonal changes are likely one of many factors affecting lean body mass and strength with aging pause.
Protein alone is not enough
Although skeletal muscle mass is important, loss of strength may be even more important, something called dynapena. In fact, we lose 2-4% strength per year which is 2-5 times faster than we lose muscle. And this can be true in individuals who maintain or even gain muscle mass.
Muscle mass has been the key defining feature of sarcopenia. Yet the latest consensus statement from the South Asian Working Action Groups on Sarcopenia (SWAG-SARCO) emphasize the significance of strength in defining sarcopenia.
A meta-analysis examined the role of protein in strength, showing that protein only improves strength when combined with resistance training, plateauing at about 1.5g/kg/BW. When people perform resistance training over several months, adding protein increases strength by about 2%.
Muscle strength occurs because of changes in hypertrophy (muscle mass) but also neural adaptations from increased use of motor units and metabolic adaptions. Resistance training affects each of these three, while protein mostly affects hypertrophy, playing a minor role in the other two. The researchers state:
Although the detailed mechanisms have not yet been elucidated, it is thought that protein intake by itself is not sufficient to induce neural and metabolic adaptations. This may be one of the reasons that protein intake alone could not effectively improve muscle strength
A group of 184 older adults (>65) were randomly assigned one of 5 interventions for a year. Body composition and strength were measured.
1) Carbohydrate supplement (30g carb)
2) Collagen protein supplement (20g pro)
3) Whey protein supplement (20g pro)
4) Light-intensity resistance training (LITW)
5) Heavy resistance with when protein (HRTW)
There wasn’t a difference in the first three. Only HRTW was effective in preserving muscle mass and increasing strength.
A follow up to this found those who continued with the resistance training after this point, whether light or heavy resistance, saw improvements compared to those who stopped. Of course, this population is older, so results may be different with midlife or younger groups.
Is more protein better or harmful?
The studies to date show that as we age, a minimum of 1.2g/kg/bw protein with aging and 1.4-2g/kg for those who exercise. To help spare lean body mass loss during weight loss, 1.6g/kg or more is recommended.
These fall into line with the Acceptable Macronutrient Distribution range of 10-35% protein. For instance, for a 140 pound woman, .8/kg/bw is 10% calories protein and 1.6/kg/bw is about 20%.
Preliminary research suggests even high protein intake 2.6-3.5g/kg/BW with resistance training can result in body recomposition, which is when weight is stable but muscle mass increases and body fat decreases.
Yet these amounts increase the percent of protein to 33-44% of calories with 165-222g per day for a 140-pound women. To obtain this, it often takes an increase in animal protein and/or protein supplementation.
Because of my food preferences (and research below) I have avoided these higher levels of protein. We need to acknowledge the potential downsides to all protein.
The potential downsides of high protein intake
Studies link higher intake of animal protein–especially red meat and processed meat — with chronic disease, particularly cardiovascular disease and cancer. These studies are imperfect, somewhat inconsistent, and can’t demonstrate cause and effect, yet I don’t think we should ignore them.
This is where plant protein has an advantage. As I pointed out in my February round-up, a study published in the American Journal of Nutrition followed 48,762 midlife nurses (<60) into older age (70-93).
The odds of aging healthily were higher in those with overall higher protein levels. When separated out, animal proteins showed a slightly less favorable link (6%) and plant proteins, a robust link to healthy aging (46%). Dairy products were also favorable to healthy aging.
This study is in line with others that look more favorably on plant protein than animal protein in terms of health outcomes. Animal proteins are preferred on high-protein diets due to their protein density and leucine levels.
Studies done on animals help explain potential watch-outs for high amounts of animal protein. A news study in Nature Metabolism combining small human trials with mice showed that consuming over 22% protein may activate immune cells through the mTOR pathway driving atherosclerotic plaque formation.
The very same amino acid that helps aid muscle protein synthesis (leucine), also can drive immune cell growth. You can’t win!
"We have shown in our mechanistic studies that amino acids, which are really the building blocks of the protein, can trigger disease through specific signaling mechanisms and then also alter the metabolism of these cells," one of the study’s researchers, Bettina Mittendorfer, Ph.D said on Science Daily. "For instance, small immune cells in the vasculature called macrophages can trigger the development of atherosclerosis."
It's important to note that this research is still in its infancy, mostly in animals, and that there are obvious upsides to protein and leucine intake. Chris Masterjon, PhD dedicated a Substack post on it and makes many important points.
“The problem is the generalizations made from this study as protein net aggravating atherosclerotic risk rather than having one extremely narrow negative role (inhibiting plaque macrophage mitophagy) amidst many positive roles (leading to a robust rate of metabolism that minimizes atherosclerosis, for example),” he said. “Rather, this finding is likely one of many downsides to being “all mTOR all the time,” and it adds to the evidence that we want to cycle through the feeding and fasting states.
In my mind, this is a “watch out” but not a deal breaker. A review of high-protein diets in prospective cohort studies found a neutral effect on cardiovascular disease, and have been found to be safe in healthy people without chronic disease.
See my other in-depth guide (for weight gain)
Summary
Protein helps midlife women maintain muscle mass and strength when part of an exercise and resistance training program. But it’s not the only aspect of diet that matters for maintaining lean body mass which I will get into in part 2.
And in my opinion, focusing only on protein in the diet is a mistake as there are some potential downsides, making a well-rounded diet and additional healthy habits important.
In my next post, I’ll talk about different options for meeting protein needs that fit your preferences as well as other nutrition tactics and timing.
Questions or comments? Let me know!