Can eating unhealthy cause muscle loss? The surprising link between diet and muscle health

October 14, 2025 •

5 min read

More than half of older adults in one study who had low protein intake also exhibited reduced muscle strength and physical performance. This highlights the stark reality that, yes, can eating unhealthy cause muscle loss, and the effects can be significant for your overall health.

Quick Summary

An unhealthy diet high in processed foods and low in vital nutrients can promote inflammation and hormonal imbalances, accelerating muscle protein breakdown and fat accumulation. When paired with inactivity, this diet choice becomes a primary driver of muscle loss.

Key Points

Poor Diet Promotes Muscle Loss: Unhealthy eating, particularly diets high in processed foods and low in protein, creates a catabolic state that breaks down muscle tissue.
Inflammation is a Key Driver: Chronic, low-grade inflammation, a result of an unhealthy diet, releases cytokines that actively trigger muscle atrophy and impair recovery.
Protein Intake is Critical: Insufficient protein, which is common in poor diets, starves muscles of the amino acids needed for maintenance and repair.
Hormonal Imbalances Interfere: Unhealthy eating can lead to insulin resistance and elevated cortisol, disrupting hormonal signals crucial for muscle growth and protection.
Processed Foods Reduce Muscle Quality: Studies show ultra-processed foods can promote fat infiltration into muscle, compromising its quality even in active individuals.
Combining Diet with Inactivity is Worst: A sedentary lifestyle amplifies the negative effects of an unhealthy diet, making muscle loss almost inevitable without the stimulus of resistance training.

While many associate a poor diet with weight gain, the truth is more complex. A steady diet of processed foods, refined sugars, and unhealthy fats does more than just add body fat; it can actively cause a catabolic state where your body starts breaking down its own muscle tissue. This process is driven by several interrelated factors, from protein inadequacy to systemic inflammation and hormonal disruption.

The Role of Protein and Nutrient Deficiency

Protein is the foundational building block for muscle repair and growth. It's composed of amino acids, and without a sufficient supply of these, especially essential amino acids like leucine, your body lacks the raw materials needed to maintain and build muscle mass.

Inadequate Protein Intake: Unhealthy diets are often calorie-dense but protein-poor. When your protein intake is too low, the body struggles to perform muscle protein synthesis (MPS) effectively, which is the process of repairing and creating new muscle. Over time, this leads to a net loss of muscle tissue.
Micronutrient Depletion: Beyond protein, a poor diet typically lacks crucial micronutrients, including vitamins and minerals essential for muscle function. For example, calcium, magnesium, and vitamin D are all critical for bone and muscle health. Deficiencies can impair muscle contraction and increase inflammation, further compromising muscle health.

Chronic Inflammation and Muscle Atrophy

One of the most insidious effects of an unhealthy diet is its contribution to chronic, low-grade inflammation. Diets high in processed foods, sugary drinks, and trans fats are particularly inflammatory.

Cytokine Release: Chronic inflammation triggers the release of pro-inflammatory cytokines, which have been directly linked to muscle atrophy. These compounds can activate signaling pathways (like NF-κB and JAK/STAT) that enhance muscle protein breakdown and suppress synthesis, leading to a significant reduction in muscle mass.
Damaged Tissues: This constant inflammatory state doesn't just affect muscles; it can harm the connective tissues that support them, like tendons and ligaments. This increases the risk of injury and impairs recovery, ultimately leading to reduced physical function.

Hormonal Imbalances Caused by Poor Nutrition

Your diet is a major regulator of your endocrine system, and an unhealthy one can throw key hormones out of balance, directly impacting muscle mass.

Insulin Resistance: Diets high in refined carbohydrates and sugar cause frequent blood sugar spikes and crashes. Over time, this can lead to insulin resistance, a condition where your cells become less responsive to insulin. Insulin is a powerful anabolic (muscle-building) hormone. Impaired insulin sensitivity reduces the uptake of nutrients by muscle cells, hampering growth and promoting breakdown.
Elevated Cortisol: Chronic stress, both from lifestyle and poor dietary choices, can elevate cortisol, a catabolic (muscle-wasting) hormone. Persistently high cortisol levels can enhance the breakdown of muscle tissue for energy, counteracting any muscle-building efforts.
Decreased Growth Hormone: Inadequate protein and poor nutrient intake can hinder the production of growth hormone, another key player in muscle repair and growth. This is especially true when paired with extreme calorie restriction.

The Unhealthy Diet vs. The Balanced Diet: A Comparison

To understand the contrast, consider the stark differences in how a diet rich in whole foods and one dominated by processed items affect your body.


Feature	Unhealthy, Processed Diet	Balanced, Nutrient-Dense Diet
Primary Goal	Provides convenience, pleasure, and energy.	Optimizes health, energy, and body composition.
Energy Source	Empty calories from refined sugar and carbs, leading to energy spikes and crashes.	Sustained energy from complex carbohydrates and healthy fats.
Protein Quality	Often low in both quantity and quality of essential amino acids.	High-quality protein sources like lean meats, fish, legumes, and eggs.
Fat Content	High in unhealthy trans fats and inflammatory omega-6s.	Balanced with anti-inflammatory omega-3s and healthy fats.
Fiber Content	Low, contributing to poor gut health and nutrient absorption.	High, supporting a healthy gut microbiome and nutrient uptake.
Micronutrient Profile	Deficient in essential vitamins (e.g., D, B vitamins) and minerals (e.g., magnesium, zinc).	Rich in micronutrients vital for muscle, bone, and immune function.
Inflammatory Impact	Promotes chronic systemic inflammation.	Contains anti-inflammatory compounds from fruits and vegetables.
Body Composition	Increases body fat, potentially through fat infiltration into muscle tissue.	Supports fat loss while preserving or building lean muscle mass.

Beyond Nutrition: The Role of Physical Activity

While nutrition is fundamental, its effects are amplified by physical activity. A sedentary lifestyle in combination with an unhealthy diet is a recipe for muscle loss and sarcopenia. Regular resistance training is the most powerful signal you can send to your body to preserve or build muscle mass. It stimulates muscle protein synthesis and counteracts the catabolic effects of poor nutrition. Without this stimulus, even a marginally unhealthy diet will favor muscle breakdown over synthesis. For optimal results, combining a healthy diet with a consistent exercise regimen is key.

Conclusion: Fueling Your Body for Strength, Not Just Survival

Eating unhealthy doesn't just make you gain fat; it can cause insidious and significant muscle loss over time by creating a catabolic environment. This is driven by insufficient protein and nutrient intake, coupled with chronic inflammation and hormonal imbalances. The dangers are particularly pronounced in the context of crash dieting and a sedentary lifestyle, accelerating a cycle of declining muscle mass and strength. To counteract this, prioritize a balanced, nutrient-dense diet that provides adequate protein, healthy fats, and complex carbohydrates. Combined with regular resistance training, this approach will help you build and maintain muscle, protect your body from inflammation, and support long-term health and vitality. For reliable nutritional information, consult resources from authoritative bodies like the World Health Organization on healthy eating patterns.

Taking Action: A Guide to Countering Muscle Loss

Prioritize Quality Protein: Aim for 20-35 grams of high-quality protein per meal to maximize muscle protein synthesis.
Balance Macronutrients: Include a mix of lean protein, healthy fats, and complex carbs to provide sustained energy and support muscle recovery.
Focus on Whole Foods: Replace ultra-processed snacks with nutrient-dense options like fruits, vegetables, whole grains, nuts, and seeds to reduce inflammation.
Integrate Resistance Training: Lift weights 2-4 times a week to stimulate muscle growth and counteract the catabolic effects of stress or poor diet.
Stay Hydrated: Proper hydration is essential for nutrient transport and muscle function.
Avoid Crash Diets: Maintain a moderate calorie deficit if trying to lose weight, as extreme restriction accelerates muscle loss.
Limit Sugar and Refined Carbs: These trigger insulin spikes that can lead to resistance and hormonal disruption.

Frequently Asked Questions

Yes, eating only junk food can cause muscle loss, even with enough calories. A diet lacking sufficient protein and essential micronutrients cannot support muscle maintenance, forcing your body to break down existing muscle tissue for amino acids. Processed foods also cause inflammation, which is known to contribute to muscle atrophy.

Chronic inflammation, often triggered by unhealthy diets, leads to muscle loss by releasing pro-inflammatory cytokines. These molecules activate signaling pathways that increase muscle protein breakdown and inhibit the protein synthesis necessary for muscle repair and growth.

Yes, crash dieting and excessive calorie deficits are highly likely to cause muscle loss. When you don't consume enough energy, your body enters 'conservation mode' and can break down muscle tissue for fuel, a process called gluconeogenesis.

Sarcopenia is the age-related loss of muscle mass and strength. An unhealthy diet can accelerate this process, particularly in older adults, by providing insufficient protein and nutrients, and promoting inflammation. Malnourished individuals are at a higher risk of developing or worsening sarcopenia.

An unhealthy diet can disrupt hormonal balance, which is vital for muscle health. It can lead to insulin resistance, reducing nutrient uptake by muscles, and increase cortisol, a stress hormone that promotes muscle breakdown.

Yes, a recent study showed that ultra-processed foods can promote fat infiltration into thigh muscles, replacing healthy muscle fibers. This compromises muscle quality and may increase the risk of conditions like osteoarthritis.

To prevent muscle loss during weight loss, focus on a moderate calorie deficit, ensure adequate protein intake (1.2-1.6g per kg of body weight), and incorporate regular resistance training. A balanced, nutrient-dense diet is key to fueling your body properly.