As cancer patients are aiming to find ways to optimize their nutrition and support their treatment and survivorship, the debate intensifies: which diet is better – the keto vs. plant-based? Both diets have gained popularity in recent years due to their reported health benefits, but they do have distinct differences. 

The keto diet involves consuming high amounts of fat, moderate protein, and minimal carbohydrates. Proponents often claim that the low-carb, high-fat approach can starve cancer cells by restricting their primary fuel source – glucose. 

On the other hand, plant-based diets focus on consuming fruits, vegetables, whole grains, and legumes. Advocates often argue that these foods are rich in antioxidants, phytochemicals, and other nutrients that can promote positive health benefits and reduce inflammation. 

While there is ongoing research, but also a great need for continued research on the effects of these diets on cancer, in this article, we delve into the science and explore the pros and cons of both diets to help cancer patients make informed decisions on fueling their fight against the disease.

Understanding the Impact of Diet on Cancer

Cancer can affect, really, anyone. But, some individuals are at higher risk than others. When it comes to cancer, there are both modifiable and non-modifiable risk factors. For the purpose of this article, we will be focusing on the modifiable risk factors. 

The American Institute for Cancer Research (AICR) and World Cancer Research Fund (WCRF) reports that “avoiding tobacco in any form, together with appropriate diet, nutrition and physical activity, and maintaining a healthy weight, have the potential overtime to reduce much of the global burden of cancer” (1). 

Furthermore, A National Health and Nutrition Examination Survey study (NHANES) “attributed more than 80,000 new cancer cases to a poor diet in the US” (2).

For the purpose of this article, we are going to primarily focus on nutrition as it relates to reducing cancer risk as a modifiable risk factor, although cancer is well-known to be multifactorial in its development. And more specifically, a keto vs. plant-based diet against cancer.

What is a Plant-Based Diet?

Although there are different variations of a plant-based diet, for the purpose of this article, we will focus on what is called a whole-food plant-based diet (WFPBD). A WFBPD focuses on nutrient dense fruits, vegetables, whole grains, and legumes while aiming to minimize processed foods, oils, and animal foods as much as possible. 

As a result, a WFPBD tends to focus on an overall nutrient and micronutrient dense (think vitamins and minerals) approach versus a focus on a specific macronutrient distribution (a specific percentage of fat, carbohydrate, and protein intake). As a result, the WFPBD nutrition approach is naturally low-fat, with adequate protein and a moderate-to-high intake of carbohydrates. 

What is the Ketogenic Diet?

A ketogenic (or, keto) diet is often confused for a low-carbohydrate diet (LCD). Although they may be similar, a keto diet requires a very specific macronutrient distribution in order to produce the production of ketone bodies – one of the fuel sources for the body created from fat in the liver, when it is lacking carbohydrates.

The macronutrient distribution in a keto diet is typically very low carbohydrate with approximately 5% of calories from carbohydrates, high fat with about 75% of calories coming from fat, and moderate protein with about 20% of calories coming from protein. 

Most ketogenic dietary approaches use meat, dairy, fish, oils, some nuts and seeds, and non-starchy vegetables to meet calorie needs in effort to promote the production of ketone bodies. 

How Might Diet Reduce Cancer Risk?

Research has identified several possibilities as to how nutrition may play a role in reducing the risk of cancer development. And it goes far beyond just “eat your fruits and vegetables”, but how certain foods or dietary patterns specifically play a role in:

• Weight
• Insulin-Like Growth Factor 1 (IGF-1) Levels
• Insulin Resistance
• Fiber
• Inflammation
• Phytochemicals
• & Short-Chain Fatty Acids

Within this article, we’ll review how the keto vs. plant-based diet may provide favorable benefits as it relates to each of these mechanisms.

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Weight Loss in the Plant-Based vs. Keto Diet

Overweight and obesity, unfortunately, increases the risk for 13 different cancers. This is likely related to increased inflammation, hormones, and growth factors associated with weight gain (1). 

When looking at both dietary approaches, both diets aim to eliminate processed foods and refined carbohydrates which are important foods to limit in the diet as both are associated with increased risk of weight gain. 

How they differ, associated with impact on weight, is that the plant-based diet is naturally less calorically dense and increases fullness when consumed, thus leading to weight loss (3). As for the keto diet, a decrease in appetite has been observed, thus resulting in lower calorie consumption and weight loss (4). 

In a 2021 inpatient, randomized crossover clinical trial (meaning the study subjects followed one dietary approach to start and switched to the other approach after) put the WFPBD and keto diet to the test. After two weeks, while on the WFPBD, individuals consumed significantly less calories and had a significant decrease in body fat. On the flip side, when adhering to the keto diet, participants lost more weight, however, most of the weight loss was a loss of lean body mass. (5) 

Weight Loss, Lean Body Mass, and Cancer

In the respects of a cancer patient, although the research is unknown at this time, the loss of lean body mass could be of great concern and a risk factor for cancer cachexia (a syndrome associated with continued decline in muscle mass [without fat loss] and can ultimately lead to functional impairment, a weakening effect of chemotherapy, and an increase in mortality [or death].) More research is needed to identify if the loss of muscle related to a keto diet could lead to this risk. (6)

As an oncology dietitian, a primary goal for our patients is to help our patients maintain muscle mass as much as possible throughout treatment and beyond as it has been shown to lead to improved outcomes during cancer treatment. 

Furthermore, long-term detrimental side effects of the keto diet need to be of consideration. Outside of potentially greater reduction in lean body mass, the keto diet is associated with higher LDL (“bad cholesterol”) levels and higher levels of fatigue (7). 

Oppositely, the WFPBD has been found to lead to significantly lower levels of LDL cholesterol and total cholesterol. (8)

IGF-1 Levels in the Plant-Based vs. Keto Diet

IGF-1, or insulin like growth factor 1, is associated with several cancers as higher levels are associated with stimulating growth (proliferation) and reducing apoptosis (or, programmed cell death of damaged and harmful cells before they can reproduce [we want this]) (9, 10).

Research has identified that individuals following a vegan diet (with similar characteristics of a WFPBD) have significantly lower levels of IGF-1 and higher levels of IGF-binding proteins 1 and 2 (think of these as scooping up or “eating up” the IGF-1 [we want this]). (10) 

It’s hypothesized these results are related to plant-protein vs. animal protein and the lower protein intake associated with a plant-based diet (Psssst – yes, lower, but adequate, intake of protein is associated with lower cancer risk). (11) 

As it relates to a keto diet and IGF-1 levels, the reduction in IGF-1 levels was not significant. (12)

Insulin Resistance in the Plant-Based vs. Keto Diet

Insulin, the hormone produced by our pancreas in response to glucose intake, is of common interest as it relates to cancer risk. High insulin levels are associated with the promotion of tumor growth (13). Thus, it is crucial to have normal, healthy levels of insulin and to ensure that insulin is working effectively (known as insulin sensitivity).

A reduction in insulin has been associated with both a WFPBD and the keto approach. (12, 14, 15)

Whereas, preclinical studies on the keto diet suggest increased insulin resistance (rather than improved insulin sensitivity, which is favorable). (16) 

Fiber in the Plant-Based vs. Keto Diet

Fiber is likely the most outstanding difference between the plant-based and keto approaches. Because fiber is only found in plant-foods and not animal foods, thus, the keto approach typically has little fiber. 

Why is fiber so important to reducing cancer risk?

A 2016 meta-analysis study (where they review the results of many studies done on the topic) reviewing 45 studies, showed a decrease is cancer death and all-cause death with 90-grams of fiber rich, whole grain intake per day (the equivalent to 3 servings per day, such as 2 slices of whole grain bread and 1 cup of cooked oats. (17) 

A higher-fiber diet has also been associated with a decrease in Ki67 – whereas higher levels of this marker are associated with cancer proliferation (the growth and progression of cancer cells) (18,19).

Fiber will also be of discussion below when we discuss short-chain fatty acids.

Inflammation in the Plant-Based vs. Keto Diets

Higher levels of inflammation are associated with increased cancer risk (and several chronic diseases). Typically when weight loss occurs, which we’ve noted does typically occur in both the WFPBD and keto approach, we commonly see reductions in inflammation. (20) 

Research has shown a reduction in inflammation with a WFPBD approach, however, although data is limited, a keto diet has demonstrated some proinflammatory effects (21, 22, 23). Further research is needed in the keto approach as it relates to inflammation.

Phytochemicals in the Plant-Based vs. Keto Diet

Phytochemicals are plant nutrients and are only found in plant foods and are thus abundant in the WFPBD approach, and limited within the keto approach. These nutrients have shown several positive benefits in reducing cancer risk such as reducing inflammation, improving the immune system, slowing the growth rate of cancer cells, and more. (1, 23, 25)

To learn more about phytochemicals and their potential role in a cancer-fighting diet, read my blog post here.

Short-Chain Fatty Acids in the Plant-Based vs. Keto Diet

What are short-chain fatty acids (SCFAs)? Great question! 

Beneficial bacteria produce SCFAs within our gut microbiome. In order for bacteria to produce these SCFAs, they require fuel, which happens to be soluble fiber and resistant starch – found, again, only in plant-foods. An example of a SCFA is butyrate. 

A diet rich in whole plant foods, like a WFPBD, is associated with higher levels of butyrate, which has demonstrated anticancer and anti-inflammatory effects. (25, 26)

As for the keto diet as it relates to SCFAs, it is associated with higher levels of the ketone body β-hydroxybutyrate (βHB) which has been shown to have similar effects as butyrate resulting in anticancer and anti-inflammatory effects. However, butyrate – like that within the WFPBD approach – has stronger anti-cancer and anti-inflammatory effects than βHB. (27) 

Although, some research has brought forward concern as to whether βHB has anticancer effects vs. pro-inflammatory and tumor progression effects (in in vitro [test tube] and in vivo [a living organism]). (27, 28, 29)

Yes, you read that right. There is some research that shows βHB may have anticancer effects and other research suggesting pro-inflammatory effects along with increased tumor progression effects. This is referred to as the “βHB paradox”. 

Whether or not this ketone body has anti- or pro- cancer effects is likely dependent on if the tumor has a “ketone metabolizing enzyme”. If that is the case, a patient may benefit from a ketogenic dietary approach. However, there is a concern that even then, a tumor may be able to adapt and develop a tolerance to a keto diet, deeming it no longer beneficial. (30) 

The research as it relates to SCFAs, the plant-based approach and its anti-inflammatory effects are relatively strong, however, further research is in great need as it relates to the ketogenic diet and βHB.

Conclusion & Summary: Choosing the Right Diet for Cancer Patients

After reviewing the current evidence available on nutrition and cancer between the WFPBD and ketogenic approach, the current data strongly supports a plant-predominant approach for both the prevention and control of cancer. 

Research suggests the plant-based dietary approach may lead to weight loss, reduced levels of IGF-1, improved insulin resistance, increased fiber intake, a reduction in inflammation, an abundant amount of phytochemicals, and the production of SCFAs as potential mechanisms as to why and how nutrition may play a substantial role in cancer prevention.

As for the ketogenic dietary approach, positively it has shown benefits against cancer in the area of weight loss, improvements in insulin, and potentially the production of βHB. However, the ketogenic diet has an association with higher levels of LDL and fatigue. And conflicting evidence exists as to if it has pro- or anti-inflammatory effects, potentially increased insulin resistance, and as to whether βHB has anticancer or proinflammatory and tumor proliferation effects. 

Research must continue in both dietary approaches. However, at this time, current research suggests favoring the plant-based dietary approach as a tool to reduce cancer risk and its recurrence – which is aligned with guidelines from the American Institute for Cancer Research and World Cancer Research Fund, American Cancer Society, and World Health Organization. 

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