One of the most frequently asked dietary questions we receive from cancer patients is: Should I eat meat? The topic of nutrition and cancer is vast and chock-full of conflicting advice. A journey through scientific studies on the subject can leave one confused. The reason for this is that there are a dizzying number of variables to consider, and dietary studies cannot control all of the variables to arrive at reliable conclusions. Basically, unlike mice, it is very difficult to test various dietary protocols in humans for more than a few weeks; retrospective studies are full of errors as people cannot recall what they eat, and not all animal protein is the same (processed verses organic wild sourced beef, cooking styles- in different oils and more).
What do the studies say?
For example, a 2019 review published in the Annals of Internal Medicine exhaustively analyzed 12 randomized trials to answer a narrow question: How does lower versus higher red meat intake affect cancer outcomes? A team of 15 reviewers looked at each study and assessed the risk of bias and the overall certainty of the evidence. Ultimately, a trial that enrolled 48,835 participants was determined to have the least bias and the most credible evidence. From this, the reviewers concluded diets restricting red meat consumption had little to no influence on cancer outcomes. Yet, the reviewers rated the evidence used to infer as low to very low certainty.(1)
Without a study that provides a robust conclusion to the meat question, we can take a reductionist approach and review the relationship between meat and cancer-related cellular pathways. The most relevant cancer-associated pathway concerning protein is known as the Mammalian Target of Rapamycin, or mTOR for short. mTOR, therefore, acts as a nutrient-sensing cellular signaling hub. When carbohydrates or specific amino acids are present, mTOR activates cell growth and proliferation. On the other hand, when nutrients are in short supply, mTOR signals the cell to transition to a protective, less proliferative state. To be sure, the occasional activation of mTOR is essential for growth and regeneration. However, in a cancer setting, it has been demonstrated that continuous or frequent mTOR activation may lead to worse outcomes, and conversely, mTOR inhibition may lead to better results. The potent mTOR inhibiting drug, rapamycin, and its analogs dramatically increase the lifespan of mice, act as a chemopreventive agent, and improve cancer outcomes.(2) While rapamycin inhibits mTOR directly, other medications can indirectly inhibit it through upstream mTOR pathways. Indeed, metformin and statins' anti-cancer activity incorporates mTOR inhibition through upstream pathways.
It is the amino acids in proteins that activate mTOR. A protein is simply a chain of amino acids linked together. After consuming protein, our digestive system breaks them down into the individual amino acids that then enter the bloodstream. Nine of the 20 amino acids are essential, meaning you can't live without them, and thus, they are critical for normal cellular regeneration and function and ultimately for survival. The chart below shows that meat is a much more concentrated source of essential amino acids than plants.
Given mTOR's prime signaling features, most researchers and dietitians who study the effect of diet on cancer suggest a moderate protein diet. The protein intake above the ideal muscle, neurotransmitter, and immunologic needs may overstimulate mTOR, causing problems. All things being equal, a person eating smaller portions of meat protein than someone eating a more considerable amount of plant proteins would approximate the same amount of total protein consumed. Given that a person has to consume protein to survive, nothing on the surface would suggest that meeting one’s protein requirements with the right portion of meat is inherently wrong.
However, cancer biology is rarely that simple. Here’s the rub: If you look at the essential amino acid composition of the meat versus plant protein chart, you can see that the two protein sources have different percentages of amino acids. So, for example, a person eating meat to satisfy their protein requirements will ingest more methionine than someone eating any equal quantity of plant protein. The question then becomes: Do specific amino acids affect cancer outcomes more than others? This topic is an active area of research. So far, preclinical research suggests that the restriction of certain amino acids may play a future role in cancer interventions, including glycine restriction, serine starvation, leucine deprivation, glutamine blockade, asparagine, and methionine restriction.(4)
One final consideration in the meat question centers on the other macromolecules packaged with plants and meat. The protein in plants tends to come packaged with carbohydrates, whereas the protein in animal protein comes packaged with fat with zero to negligible carbohydrates. While fat is neutral regarding mTOR, carbohydrates are not: carbohydrates activate mTOR through a secondary pathway involving insulin. Concerning our original question, this changes the calculus because now we must consider insulin's role in cancer outcomes. Insulin management is a very active area of research. Ketogenic diets, or "insulin suppressing" diets that consist of high fat, low carbohydrate, and moderate protein, are being studied as an adjuvant therapy for cancer. The list below shows the quantity of carbohydrates in some of the more protein-rich plant foods:
Vegetable: Protein (g) Fat (g) Carbohydrates (g)
Tofu 8.8 4.8 2.4
Tempeh 8.9 5.4 2.2
Edamame 9.1 1.9 17.3
Lentils 8.8 0.6 20.2
Chickpeas 7.2 1.6 26.9
Black beans 7.7 1.3 22.2
Kidney beans 7.8 0.8 22.8
Navy beans 7.3 0.4 23.4
Peas 6.3 0.6 19.2
Spinach 3.4 0.4 7.7
Broccoli 2.8 0.4 5.1
Brussels spts 2.8 0.2 4.5
USDA National Nutrient Database for Standard Reference Release 28. The serving sizes are as follows: tofu (100g), tempeh (100g), edamame (1 cup), lentils (1 cup), chickpeas (1 cup), black beans (1 cup), kidney beans (1 cup), navy beans (1 cup), peas (1 cup), spinach (1 cup cooked), broccoli (1 cup cooked), Brussels sprouts (1 cup cooked).
The idea of "starving" cancer through diet is seductive for researchers and patients. However, like all therapeutic interventions (chemotherapy and radiation), the challenge has always been the large degree of overlapping biology between cancer and healthy cells. Overzealous avoidance of animal protein can have the paradoxical outcome of protein malnutrition aiding cachexia, which is the cause of death in an estimated 20% or more of cancer patients. Additionally, a meat avoidance cancer mindset may foster excessive carbohydrate intake through plant proteins to meet protein minimums, leading to overstimulation of mTOR through high insulin levels. Finding therapeutic interventions that can exploit the differences remains the hurdle for all new interventions. Dietary strategies face the same obstacle. Cancer cells and healthy cells require the same amino acids – the goal for researchers is to tease out the amino acids that cancer cells rely upon more heavily and that healthy cells can adapt to some degree of deficiency.
A new company called Faeth Therapeutics is doing just that. They are actively recruiting for clinical trials on highly specialized diets comprised of specific ratios of amino acids, fats, and carbohydrates depending on the unique metabolism of different cancer types. We are paying close attention to these trials and will update everyone on the results when available.(5)
As for the original question: Should cancer patients eat meat?
Given our current literature, there is no evidence to conclude that obtaining appropriate protein requirements through quality non-processed meat is a problem for cancer patients. Meakin Metabolic Care strives to balance these concerns through modified ketogenic diets incorporating cleanly sourced animal protein and protein supplements, intermittent fasting, targeted exercise, repurposed drugs, vitamins, and lifestyle optimization. We have created a platform that minimizes your cost and valuable time available in 45 states.
Summarizing the research:
A review of clinical trials that explored the effect of red meat on cancer outcomes concluded that lower versus higher red meat consumption had little to no impact on cancer outcomes. However, the review also concluded that the evidence used to conclude provided low certainty.
Most researchers and dietitians suggest a moderate protein diet because excess protein intake may activate the well-established cancer-promoting mTOR pathway.
Ongoing clinical trials may lead to “designer” diets for cancer patients that have specific rations of amino acids, fats, and carbohydrates depending on the cancer type.
Meakiin Metabolic Clinic suggestions
Given the current body of knowledge, eating a diet of moderate protein content is advisable for cancer patients.
There is no definite evidence to suggest that meeting these requirements with some portion of meat will lead to worse outcomes and pursuing plant sources only has challenges as discussed above.
Stay strong and keep smiling and be your own best doctor,
- Chuck
Charles J. Meakin MD, MHA, MS
Disclaimer: This information is not meant as direct medical advice. Readers should always review options with their local medical team. This is the sole opinion of Dr. Meakin based on a literature review at the time of the blog and may change as new evidence evolves.
1 - Zeraatkar D, Johnston BC, Bartoszko J, Cheung K, Bala MM, Valli C, Rabassa M, Sit D, Milio K, Sadeghirad B, Agarwal A, Zea AM, Lee Y, Han MA, Vernooij RWM, Alonso-Coello P, Guyatt GH, El Dib R. Effect of Lower Versus Higher Red Meat Intake on Cardiometabolic and Cancer Outcomes: A Systematic Review of Randomized Trials. Ann Intern Med. 2019 Nov 19;171(10):721-731. doi: 10.7326/M19-0622. Epub 2019 Oct 1. PMID: 31569236.
2 - Blagosklonny MV. Cancer prevention with rapamycin. Oncotarget. 2023 Apr 14;14:342-350. doi: 10.18632/oncotarget.28410. PMID: 37057884; PMCID: PMC10103596.
3 - Comparison profile of amino acids table: https://geneticliteracyproject.org/2020/10/05/should-you-get-your-protein-from-plants-or-animals-short-nutrition-lessons-shows-thats-the-wrong-question/
4 - Kang JS. Dietary restriction of amino acids for Cancer therapy. Nutr Metab (Lond). 2020 Mar 14;17:20. doi: 10.1186/s12986-020-00439-x. PMID: 32190097; PMCID: PMC7071719.
6 - "Cancer Cachexia: A Review of Pathophysiology, Clinical Manifestations, and Treatment" by S.K. Verma and A.K. Aggarwal, published in the Journal of Cachexia, Sarcopenia and Muscle in 2015.