The carnivore diet, a highly restrictive eating pattern consisting entirely of animal products, has gained popularity for its purported health benefits. However, its role in cancer prevention and treatment remains a subject of intense debate and ongoing research. This article delves into the existing evidence, examining both the potential benefits and risks associated with the carnivore diet in the context of cancer.
Historical Context of Dietary Interventions in Cancer
The concept of using diet as a therapeutic intervention dates back centuries. As early as 500 BC, fasting was employed as a treatment for various medical conditions. In the early 20th century, Guelpa and Marie proposed fasting as an antiepilepsy treatment. Woodyatt observed that starvation or high-fat, low-carbohydrate diets led to the production of acetone and β-hydroxybutyrate, alternative energy sources produced by the liver in the absence of glucose.
The ketogenic diet (KD), a low-carbohydrate, high-fat diet mimicking the metabolic effects of starvation, emerged as an alternative to fasting. Wilder and Peterman formulated the fat-to-carbohydrate ratio still used today: 1 g protein per kg of body weight in children and 10 to 15 g carbohydrates daily, with fat comprising the remainder of calories.
In 1922, Braunstein noted the disappearance of glucose from the urine of diabetic patients after cancer diagnosis, suggesting glucose recruitment to cancerous areas. Nobel laureate Otto Warburg found that cancer cells thrive on glycolysis, producing high lactate levels even with abundant oxygen. While KD use in epilepsy treatment and cancer research waned by the mid-20th century, it regained recognition in the mid-to-late 1990s.
The Carnivore Diet: An Overview
The carnivore diet is an extreme, restrictive eating plan that eliminates all plant-based foods, focusing exclusively on animal products such as meat, fish, eggs, and select dairy products. This means excluding all fruits, vegetables, grains, legumes, nuts, and seeds.
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The rationale behind the carnivore diet lies in the metabolic shift that occurs when carbohydrate intake is severely restricted. The body enters a state of ketosis, where it burns fat for energy and produces ketones. Proponents claim this metabolic state leads to rapid weight loss, stable blood sugar, and reduced inflammation.
Ketogenic Diet Metabolic Pathways
Ketogenic diets mimic the fasting state, wherein the body responds to the lack of glucose by producing ketones for energy. Excess lactate production, which is part of the Warburg effect, compensates for ATP production defects caused by dysfunctional mitochondrial oxidative phosphorylation. The resulting tumor dependence on glucose can be exploited with KD use. In KDs, the 4:1 ratio of high fat to low carbohydrates mimics the metabolic effects of starvation. These diets slow cancer by inhibiting insulin/IGF and downstream intracellular signaling pathways, such as phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR). Ketogenic diets also amplify adenosine monophosphate-activated protein kinase (AMPK), which inhibits aerobic glycolysis and suppresses tumor proliferation, invasion, and migration.
Potential Benefits of Ketogenic Diets in Cancer Research
Targeting Cancer Metabolism
Cancer cells often exhibit dysfunctional mitochondria and electron transport chain defects, disrupting normal adenosine triphosphate (ATP) production. When glucose is scarce, the body produces ketones and fatty acids, which provide energy for normal cells but may not benefit cancer cells.
Inhibiting Growth Pathways
KDs slow cancer by inhibiting insulin/IGF and downstream intracellular signaling pathways, such as phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR). They also amplify adenosine monophosphate-activated protein kinase (AMPK), which inhibits aerobic glycolysis and suppresses tumor proliferation, invasion, and migration.
Inducing Ferroptosis
In mice with pancreatic and colorectal cancer, keto diets slow the growth of tumors by a process called ferroptosis. This kills the cancer cells by causing a lethal buildup of toxic fatty molecules.
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Evidence from Studies
Researchers first treated pancreatic cancer with a cancer drug called eFT508 that disables eIF4E, intending to block tumor growth. Knowing that pancreatic cancer can thrive on fat, and that eIF4E is more active during fat burning, the scientists first placed the animals on a ketogenic diet, forcing the tumors to consume fats alone, and then put them on the cancer drug.
In mice with colorectal cancer, a ketone molecule called beta-hydroxybutyrate (BHB), produced during low-carb diets, slows tumor growth.
Risks and Concerns Associated with the Carnivore Diet in Cancer
Increased Risk of Certain Cancers
The carnivore diet relies heavily on red and processed meats, which have been linked to an increased risk of cancer, particularly colorectal cancer.
Gut Microbiome Disruption
The absence of plant-based foods can disrupt the gut microbiome, increasing inflammation throughout the body, a known cancer risk factor.
Nutrient Deficiencies
The restrictive nature of the carnivore diet can lead to vitamin and mineral deficiencies.
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Kidney Stress
Consuming a large amount of animal protein can put unwanted stress on the kidneys, especially in individuals with pre-existing kidney issues.
Cachexia
In mice with pancreatic and colorectal cancer, keto accelerates a lethal wasting disease called cachexia. Patients and mice with cachexia experience loss of appetite, extreme weight loss, fatigue, and immune suppression.
Lack of Fiber
The absence of dietary fiber in the carnivore diet is a concern, as higher fiber consumption is associated with a lower risk of colon cancer.
Red Meat and Processed Meat Consumption
People with the highest level of red meat intake had a 30% increased risk for colorectal cancer; those with the highest level of processed meat intake had a 40% increased risk.
Heterocyclic Amines
Possible mechanisms underlying epidemiological associations include the formation of heterocyclic amines in meat when it is cooked. These heterocyclic amines require acetylation by P450 enzymes, and individuals with the fast-acetylating genotype who eat high amounts of meat may be at increased risk of large-bowel cancer.
Counterarguments and Considerations
The Role of Trans-Vaccenic Acid (TVA)
A nutrient called trans-vaccenic acid (TVA), found in food products from grazing animals, has shown promise in promoting T cell activity. Studies have demonstrated that TVA can inactivate a receptor on the cell surface called GPR43, activating a cellular signaling process known as the CREB pathway, involved in cellular growth, survival, and differentiation.
The Importance of Metabolomics
Research highlights the promise of a "metabolomic" approach to understanding how the building blocks of diet affect health. After millions of years of evolution, only a couple hundred metabolites derived from food end up circulating in the blood, suggesting their importance in biology.
Addressing Cachexia
Pairing keto with common drugs called corticosteroids prevented cachexia in mice with cancer.
Clinical Trials and Ongoing Research
Several clinical trials are underway to investigate the effects of ketogenic diets on cancer. Duke University has initiated a randomized study of the Atkins diet and androgen deprivation therapy for patients with prostate cancer. Tel Aviv Sourasky Medical Center in Israel is recruiting previously treated chemoradiation patients with high-grade glial tumors for an open-label study of the efficacy of KD in preventing tumor growth and recurrence. St. Joseph’s Hospital and Medical Center (Phoenix, AZ) is recruiting newly diagnosed glioblastoma patients for a phase 1/2 prospective trial involving upfront resection followed by KD with radiotherapy and concurrent temozolomide, followed by adjuvant temozolomide chemotherapy.
Expert Opinions and Recommendations
Experts emphasize that the best diet for cancer prevention includes plenty of plant foods. This doesn’t mean you can’t eat meat, but it means making meat a supporting player rather than the star of every meal. Choose lean proteins like fish and poultry more often than red meat, and when you do eat red meat, keep portions moderate and pair them with colorful vegetables and whole grains.