For years, the story around animal protein was simple: eat too much, and you might be increasing your risk of cancer and chronic disease. The concern came from its effect on IGF-1, a growth factor linked to tumor development. More protein meant more IGF-1, which was assumed to mean more tumors.

That was the prevailing wisdom for decades. But new evidence tells a different story.

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## The Old Fear: Protein and IGF-1

IGF-1 (insulin-like growth factor 1) plays a role in growth and cell proliferation. Researchers worried that higher [protein](/nutrients/protein) intake, especially from animal sources, would raise IGF-1 levels and thereby increase cancer risk.

It made sense on paper — more protein → higher IGF-1 → more uncontrolled growth. But the science didn't fully back this up.

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## What the Research Actually Shows

A large 18-year study of nearly 16,000 U.S. adults found **no link** between [protein](/nutrients/protein) intake, IGF-1 levels, and death from cancer, heart disease, or any other cause (Moradi et al., 2023).

In fact, the researchers found something surprising: people who ate more animal protein showed a **modest protective trend against cancer mortality**. Instead of being harmful, higher protein intake appeared neutral — or even slightly beneficial.

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## What is beneficial with animal protein?

Animal protein–rich foods often provide critical nutrients that many people don't get enough of, including:

- **[Omega-3 fatty acids](/nutrients/omega-3)** – anti-inflammatory fats that support heart, brain, and muscle health.
- **[Vitamin B12](/nutrients/vitamin-b12)** – essential for energy metabolism, red blood cells, and cognitive function.
- **[Iron](/nutrients/iron) (heme iron)** – the most bioavailable form of iron, crucial for oxygen transport.
- **[Zinc](/nutrients/zinc)** – important for immune defense and cellular repair.
- **[Vitamin D](/nutrients/vitamin-d)** – found in fatty fish, eggs, and dairy, it plays a central role in bone strength, immune health, and hormone regulation.

Together, these nutrients contribute to healthier aging and may help explain why higher protein intake sometimes shows a protective trend in research.

Beyond nutrient content, protein itself provides benefits such as:

- Preserving **muscle mass and strength** — key for mobility and independence as we age.
- Supporting **metabolic health**.

Without enough protein, we lose muscle and resilience more quickly — a process that accelerates over time.

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## How Much Protein Do You Need?

Experts generally recommend **0.7–1g of protein per pound of ideal body weight per day** (roughly ~100g for many adults).

Just as important is **balancing protein with plants**: colorful vegetables, fruits, legumes, and whole grains provide [fiber](/nutrients/fiber), antioxidants, and phytonutrients that complement the benefits of protein.

If you're unsure if you're getting enough protein in your diet, you can track your protein intake amongst other nutrients with Microgram.

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## Bottom Line

Instead of fearing animal protein, the focus should be on **quality** and **balance**. Adequate, nutrient-rich protein isn't likely to shorten your life — it may, in fact, support it.

Grass-fed meats, eggs, poultry, and wild-caught fish can play a positive role when combined with a diet rich in plant foods. The key takeaway from the latest research: protein is not the enemy.

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## Sources

- Moradi, S., et al. (2023). Animal and plant protein usual intakes are not adversely associated with all-cause, cardiovascular, or cancer-related mortality risk in U.S. adults (NHANES III). *Appl Physiol Nutr Metab, 49*(2), 120–130.
- Guasch-Ferré, M., et al. (2020). Dietary protein intake and risk of mortality: NHANES III cohort. *Am J Clin Nutr, 111*(3), 594–604.
- Sandhu, M. S., et al. (2002). Insulin-like growth factor I (IGF-1) and risk of cancer. *The Lancet, 360*(9346), 1348–1356.
- Coelho-Júnior, H. J., et al. (2022). Effects of protein supplementation on muscle mass and function in older adults: systematic review and meta-analysis. *Nutrients, 14*(4), 786.

Animal Protein: Harmful or Protective? What the Latest Science Says

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