In depth
Inflammatory myositis and diet
Protein comes up all the time in a disease that wastes muscle, and it's the first thing people ask about. What the trials here tested was resistance training. That's where the muscle gains came from, and the protein question recurs through the training question, which is why this page is shaped the way it is.
What the research found.
One randomized trial tested high-intensity resistance training in people who had myositis. The physical score on the SF-36, a general patient-reported quality-of-life questionnaire, improved by 5.33 points, muscle endurance improved by 11.49 points, and muscle testing improved by 1.30. All three were between-group results, and all three of them reached statistical significance.
That trial reported no rise in disease activity at all, and creatine kinase didn't spike over the 16 weeks. At one year the muscle endurance gain was 10.7 points between groups. The true value ranges from 2.2 to 19.1, which is a wide interval around a gain that is real.
Anybody starting or staying on long-term corticosteroids is covered by the 2017 American College of Rheumatology guideline. It asks for enough calcium and vitamin D, for weight-bearing and strength-building exercise, for stopping smoking, and for limiting alcohol. That advice reaches a reader through their treatment rather than through their diagnosis.
One review pooled the exercise trials that have been run in dermatomyositis and polymyositis. Strength improved at a standardized mean difference of 0.62, and aerobic fitness improved alongside it in those trials. The evidence behind both of those figures was rated low certainty, because the samples going into it were small ones.
What has been tested here, and what hasn't
No nutrition trial exists in myositis at all. That's a documented absence rather than a hole in this site's reading of the literature. So any dietary advice given for this diagnosis has been borrowed from somewhere else.
What has been tested, and tested well for a rare disease, is exercise. One randomized trial used high-intensity resistance training, where the physical score on the SF-36, a general patient-reported quality-of-life questionnaire, improved by 5.33 points between groups, muscle endurance improved by 11.49 points, and manual muscle testing improved by 1.30. All three reached significance, disease activity didn't rise, and creatine kinase didn't spike over the 16 weeks.
At one year the muscle endurance gain was 10.7 points between groups, on a true value ranging from 2.2 to 19.1. That counts on a page about diet, because people ask two nutrition questions in a muscle disease. They ask about protein and about vitamin D, and the answer to the first recurs through training.
Protein, and why the training comes first
Protein supports muscle when you train as well, and without the training extra protein is mostly wasted. That's how bodies work in general rather than a finding in this particular condition. It's also the most useful thing to know about the question.
So this page points at the resistance training evidence instead of the food. The trials in myositis that produced muscle gains produced them by training people. No trial has tested whether adding protein to that changes the result, and no trial has tested whether protein on its own does anything at all.
How much protein a person needs depends on several different things. It depends on body size and age, on how much resistance training they're doing, and on whether they take corticosteroids, which speed up muscle breakdown. Kidney function is the limit in the other direction, and anybody with kidney disease needs their own target from the clinicians managing it.
This site gives no protein figure at all, in this or in any other condition. Nothing has been supplied that it can attribute to a source. A number without a source behind it is the one thing this site refuses to print anywhere at all.
Vitamin D, which is about bone here
The vitamin D advice for somebody with myositis reaches them through the treatment rather than through the disease. Anybody starting or staying on long-term corticosteroids falls under the 2017 American College of Rheumatology guideline, which is strong across every age group there is. It asks for enough calcium and vitamin D, for weight-bearing and strength-building exercise, for stopping smoking, and for limiting alcohol.
That advice is about protecting bone during corticosteroid treatment, and it's a real reason to attend to your vitamin D. It's a different claim from vitamin D building muscle strength. That has never been shown in this disease, and it has never been tried.
Notice what else falls inside that piece of advice. It lists weight-bearing and strength-building exercise right alongside the nutrients rather than instead of them. That's the conclusion the myositis trials reached by a completely different route of their own.
Swallowing, which is the practical dietary problem
Trouble swallowing is a known feature of this disease group, and it's the food problem most likely to affect somebody's nutrition in practice. It changes which textures are manageable, it makes meals slower and more tiring, and people work around it. That working around is where intake falls without anybody noticing it happening.
Avoiding hard textures limits what gets eaten each week. The drop happens slowly enough that it doesn't feel like a change worth mentioning to anybody. So it goes unreported, and the weight comes off for a reason that has never been looked at properly.
This site holds no source on managing it, which is a real hole on a page like this one. What it can say here is short enough. Trouble swallowing is a feature of the disease and not a habit, so it's worth raising with your team by name.
Weight during corticosteroid treatment
Corticosteroids put weight on, and it's one of the most disliked things about taking them. Wanting to cut back sharply on food makes complete sense. In this disease that deserves rather more caution than usual, because muscle is the tissue already at risk of wasting away.
Cutting food out sharply risks losing the very thing that resistance training is there to protect in the first place. The better approach pairs what you eat with the strength work. That's why those two fall inside one piece of advice rather than standing as alternatives to each other, and the guideline puts them together for that reason.
Unintended weight loss is worth mentioning, and it isn't progress of any kind. This disease wastes muscle, so losing weight you didn't set out to lose is a reason to be assessed by somebody. It isn't a sign that something has started working.
Common misconceptions.
Myth. Eating more protein will rebuild my muscle.
Reality. Protein supports muscle when you train as well, and without the training extra protein is mostly wasted. What was tested in this disease was the training, where resistance work improved muscle endurance by 11.49 points and muscle testing by 1.30 between groups. So the protein is what makes those gains possible rather than what produces them.
Myth. There's a diet for myositis.
Reality. No food trial has been run in this disease at all. Protein and vitamin D come up a great deal, and there's a reason for that, because this disease wastes muscle and corticosteroids do too. Neither of them has been tested here, so any firm food rule you're given is borrowed from some other disease or from general food writing.
Myth. Vitamin D will help my muscles directly.
Reality. Nothing in this disease has tested that question. The vitamin D advice you get comes from the corticosteroid guideline, where it's about your bones, because corticosteroids thin bone and vitamin D helps guard it. That's a real reason to attend to it, and it's a different claim from building muscle, which no study here has shown.
Myth. I should avoid protein because of my kidneys.
Reality. Kidney disease does change how much protein you need, so it's a reason for your own target rather than a general one. Get that target from the clinicians managing your kidneys. This site gives no protein figure at all, in this or any condition, because nothing has been supplied that it can attribute to a source.
Cautions specific to this condition.
- Combine any protein change with resistance training. The training is what produced the muscle gains in the trials. Protein alone wasn't tested.
- Ask about calcium and vitamin D at the start of corticosteroid treatment. The guideline applies from the day a long course begins.
- Get your own protein target if you have kidney disease. It should come from the clinicians managing your kidneys, not from a general figure.
- Mention trouble swallowing, because working around it without saying so is how people lose weight without meaning to. It changes what you can eat, and it's a feature of the disease and not a habit.
- Watch your weight during corticosteroid treatment. Be careful about cutting food out sharply. Muscle is already the tissue at risk here.
- Tell your team about supplements. Interactions are real, and they're rarely printed on the label.
Discuss any change with the rheumatologist who manages your care. Nothing here replaces that conversation.
Questions patients ask.
Is there a diet for myositis?
No food trial has been run in this disease, and that absence is in the literature rather than in what this site has read. Protein and vitamin D still come up a great deal, because this disease wastes muscle and long corticosteroid use does too, so both sound like they should count. Neither of them has been tested here, so any firm food rule you're given is borrowed from somewhere else.
Should I be eating more protein?
Protein supports muscle when you train as well, and without the training extra protein is mostly wasted. That's general physiology rather than a finding in this disease. What was tested here was the training, where resistance work improved muscle endurance by 11.49 points and muscle testing by 1.30 between groups, without creatine kinase spiking over 16 weeks.
How much protein should I have?
This site gives no figure at all, in this or any condition, because nothing has been supplied that it can attribute to a source. What moves your own target is body size and age, how much resistance training you're doing, whether you're on corticosteroids, and your kidney function. Only the clinicians managing your kidneys can set that last one.
What about vitamin D?
The advice that applies to you comes through the corticosteroid rather than through the muscle disease. Anybody starting or staying on long-term corticosteroids falls under the 2017 American College of Rheumatology guideline, which asks for enough calcium and vitamin D, weight-bearing and strength-building exercise, stopping smoking, and limiting alcohol. That's about protecting bone, which is a different reason from helping muscle.
Does anything I eat affect my creatine kinase?
Nothing in this disease has tested that question. What's known here is about exercise, because one trial used hard weight training for 16 weeks and creatine kinase didn't spike, which is what most people want to know before they start. Creatine kinase also goes up after any hard effort in people with no muscle disease, so a single reading is hard to read.
Swallowing has become difficult. Does that change what I should eat?
It changes what you can eat, and it's worth mentioning. Trouble swallowing is a known feature of this disease group rather than a habit or a nuisance, and it can cut your intake a great deal once you start avoiding textures. This site holds no source on managing it, which is a real hole, so raise it as its own problem.
Should I lose weight if steroids have put it on?
Go slowly, and keep an eye on muscle while you do. Muscle is the tissue this disease puts at risk, and cutting food back hard can cost you the very thing the weight training is there to save. The corticosteroid guideline asks for the nutrients and for weight-bearing and strength work at once, which is why doing both beats cutting food alone.
References.
- Jensen KY; Aagaard P; Suetta C et al. High-intensity resistance training improves quality of life, muscle endurance and strength in patients with myositis: a randomised controlled trial. Rheumatology international. 2024;44:1909-1921. 10.1007/s00296-024-05698-yRCT
- Jensen KY; Aagaard P; Suetta C et al. High-intensity resistance training in patients with myositis - 1-year follow-up on a randomised controlled trial. Rheumatology international. 2025;45:104. 10.1007/s00296-025-05858-8RCT follow-up
- da Silva BISL; Dos Santos BRJ; Carneiro JA et al. Physical exercise for dermatomyositis and polymyositis: a systematic review and meta-analysis. Clinical rheumatology. 2022;41:2635-2646. 10.1007/s10067-022-06281-1SR + MA
- Buckley L; Guyatt G; Fink H et al. 2017 American College of Rheumatology Guideline for the Prevention and Treatment of Glucocorticoid‐Induced Osteoporosis. Arthritis & Rheumatology. 2017;69:1521-1537. 10.1002/art.40137GRADE-based clinical practice guideline
This page gathers the published research on this subject into one place. The studies behind it were published between 1989 and 2026, and every figure links to the paper it came from. Those studies were peer reviewed. This summary of them was not. Dr. Sarah Luebker is reviewing these pages one at a time and has not reached this one yet, so it carries no medical review date and nothing here is her opinion or her advice to you. Each page gets updated as she reaches it. It is here in the meantime because the science is worth having in one organized place that is easy to find and easy to read. Talk to your own clinician before acting on any of it.