Does Food Quality Affect Muscle Quality?

Bad News for your Dirty Bulk: Highly Processed Food Impacts Muscle Quality

Does Food Quality Affect Muscle Quality?

A new study suggests it does. The National Health Institute conducted a study under the Osteoarthritis Initiative, which revealed surprising results about food quality’s impact on muscle quality.

You’ve probably heard of a dirty bulk. Healthline.com defines “dirty bulking [as] an intense period of weight gain to support strength and muscle gains. There are no limitations on food, and high-calorie shakes and gain powders are often used.”

‘Dirty Bulking’ is commonly used in the bodybuilding and fitness community as a way of gaining muscle fast—it’s cheap, convenient, and driven by the principle of “If It Fits Your Macros” (IIFYM) which argues that as long as your calories and macronutrients are in balance (your protein, fat, and carbohydrates), then it doesn’t matter what or how much you eat. 100 grams of protein is 100 grams of protein—who cares if it’s coming from a chicken breast or a double bacon cheeseburger? At the end of your ‘bulking’ phase, you will have gained the mass and muscular strength that you had set out to achieve, the same as if you had done a ‘clean bulk’ with minimally processed foods. 

Not so fast! Unfortunately for all the dirty bulkers—and for every fitness enthusiast with a penchant for junk food—a new study is undermining the IIFYM strategy, as it seems that food quality does indeed affect muscle quality. So you might want to rethink that post-work McDonald’s visit! 

Performed by the National Health Institute in their nationwide (United States) Osteoarthritis Initiative, the researchers used a participant pool of 666 individuals (455 men, 211 women) who were not yet affected by osteoarthritis (based on MRI imaging) to study the effects of diet on knee arthritis, and “on average, participants were overweight with a body mass index (BMI) of 27. Approximately 40% of the foods that they ate in the past year were ultra-processed”. This imaging study was the first to look into the relationship between MRI-based skeletal muscle quality and quality of diet. 

The researchers found a positive link between a diet high in ultra-processed food and greater levels of intramuscular fat. More intramuscular fat usually results in poor muscle quality. In short, the more ultra-processed foods that people consumed, the more intramuscular fat they had in their thigh muscles. These results held true even controlling for age, BMI, socioeconomic factors, activity level and dietary calories. And while this study only looked at the muscles in the thighs, we might guess that muscles throughout the body would be affected—which would be an interesting hypothesis for a future study! 

Key Findings of the Study:

• Researchers studied 666 participants (455 men, 211 women) without osteoarthritis.
• Participants had an average BMI of 27 and consumed diets where 40% of foods were ultra-processed.
• MRI scans revealed a positive correlation between ultra-processed foods and intramuscular fat, which leads to poor muscle quality.

What Are Ultra-Processed Foods?

Are you confused about the difference between “processed” versus “unprocessed” food? “High processed” or “ultra-processed” foods include not only most fast-food meals, but “breakfast cereals, margarines/spreads, packaged snacks, hot dogs, soft drinks and energy drinks, candies and desserts, frozen pizzas, ready-to-eat meals, mass-produced packaged breads and buns, and more”. Some processed foods can be healthy, such as most types of tofu, canned beans and legumes, etc. If you’d like more information on the different types of processed food, The Heart and Stroke foundation offers some helpful definitions and advice in their article here. As you are probably aware, muscle quality is not the only thing negatively affected by a diet high in ultra-processed foods. There are many correlations between highly-processed foods and negative health conditions, such as stroke and cognitive decline and poor heart health.

Understanding the difference between processed and ultra-processed foods is crucial for making healthier choices.

Examples of Ultra-Processed Foods:

• Fast food meals (e.g., burgers, fries, soft drinks)
• Packaged snacks (e.g., chips, candies)
• Frozen pizzas and ready-to-eat meals
• Sugary cereals, energy drinks, and desserts

Examples of Healthy Processed Foods:

• Canned beans and legumes
• Most types of tofu
• Whole grain breads with minimal additives

So, what can we do to reduce our intake of ultra-processed foods? We’re not always able to make minimally processed and ‘healthy’ meals for ourselves—maybe you’re on a trip, or short on time, or just really, really busy. Thankfully, if you live in a city, there are plenty of fast-food establishments that offer healthier options, such as salads and wraps. Even grocery stores have ‘to go’ meals that are minimally processed. If you’re in North America, this list compiled by registered dieticians offers suggestions for healthy fast-food options (and it’s printable!). Remember, reducing your ultra-processed food intake by even a small percentage can result in a huge positive impact on your health. There are countless resources, both online and in person, that are available to help you make easy, healthy dietary choices, including Infofit’s Sports Nutrition course.

Why You Should Avoid Ultra-Processed Foods

Ultra-processed foods don’t just affect muscle quality—they’re linked to:

• Cognitive decline
• Heart disease
• Stroke risk

Making small changes to reduce your intake of ultra-processed foods can significantly improve your overall health.

Tips to Reduce Ultra-Processed Food Intake

Even if you’re busy, there are ways to make better food choices:

1. Healthier Fast-Food Options: Many restaurants offer salads, wraps, and grilled protein options.
2. Grocery Store ‘To-Go’ Meals: Many supermarkets provide ready-to-eat meals with minimal processing.
3. Plan Ahead: Batch cooking and meal prepping can help ensure you have healthier options readily available.

Takeaway: Better Food, Better Muscle Quality

Rethinking dirty bulking and prioritizing food quality can improve muscle health and overall wellness. Start small—every positive change adds up.

Wishing you all the best on your journey to optimum health! 

​​Written by Theresa Faulder, Master’s in English, Certified Personal Trainer and Infofit fitness blog writer.

Works Cited

NutriProCan, says, M., says, C. A., says, S., says, K., & says, C. H. (2024, August 26). Your Best Fast Food Picks for 2024: A Comprehensive Guide By Registered Dietitians!. NutriProCan. https://nutriprocan.ca/2024-fast-food-picks/ 

Preiato, D. (2019, December 5). Dirty bulking: Effectiveness, downsides, and more. Healthline. https://www.healthline.com/nutrition/dirty-bulking 

Rahemi, H., Nigam, N., & Wakeling, J. M. (2015, August 6). The effect of intramuscular fat on skeletal muscle mechanics: Implications for the elderly and obese. Journal of the Royal Society, Interface. https://pmc.ncbi.nlm.nih.gov/articles/PMC4535407/ 

ScienceDaily. (2019, November 11). Too much ultra-processed food linked to Lower Heart Health. ScienceDaily. https://www.sciencedaily.com/releases/2019/11/191111084920.htm 

ScienceDaily. (2024a, May 22). Eating more ultra-processed foods tied to cognitive decline, stroke, according to study. ScienceDaily. https://www.sciencedaily.com/releases/2024/05/240522225300.htm 

ScienceDaily. (2024b, December 4). Eating high-processed foods impacts muscle quality, study finds. ScienceDaily. https://www.sciencedaily.com/releases/2024/12/241204145421.htm 

What is ultra-processed food? Heart and Stroke Foundation of Canada. (n.d.). https://www.heartandstroke.ca/articles/what-is-ultra-processed-food