Diet and Renal Cell Carcinoma Risk

Review of Int J Cancer. 2005;113(3):451-55.

A study in the International Journal of Cancer looked at how diet and nutrition may be related to risk of renal cell carcinoma (kidney cancer). This study suggests that eating a diet that contains more than 5 servings of vegetables and fruit per day may decrease risk of renal cell carcinoma by approximately 40%. In particular, eating more root vegetables (carrots & beets) appeared to reduce renal cell cancer risk the most. We provide PRACTICAL information on what these findings mean, including ideas for getting more of these healthy foods into your diet. Factors such as age, gender, and family history cannot be changed, but diet and nutrition can! This information can help individuals take concrete and practical steps that may decrease their risk of kidney cancer. 

Note: Numbers appearing at the end of sentences indicate research references. References are listed at the end of each article.

Background

Over 80% of kidney cancers in adults are a type of cancer known as renal cell carcinoma. Despite the fact that renal cell cancer causes about 2% of all cancer-related deaths in the United States (1), the factors that may increase the risk of this cancer are not well understood. Recognized risks for renal cell cancer include a family history of the disease, smoking, and being overweight or obese (2-5). However, these factors only account for about half of all cases of this disease (3). For this reason, it is important that researchers continue to study renal cell cancer and try to determine ways to reduce risk of this disease.

A study published in the International Journal of Cancer looked at how diet and nutrition may be related to risk of renal cell carcinoma (kidney cancer) (6). It is hoped that this type of research will help identify the best type of diet for reducing risk of this disease.

What The Researchers Studied

In order to examine the connection between what people eat and risk of renal cell cancer, researchers collected information on diet and nutrition habits from 61,000 Swedish women who were 40 to 76 years old at the start of the study (6). Information on other important health-related factors including age, height and weight, education level, and smoking was collected and accounted for in the study. The researchers followed the women in this study for an average of 13.4 years. The researchers then used all of this information to explore how diet and nutrition may be related to risk of developing renal cell carcinoma (kidney cancer).

What The Study Found

First, the researchers found that women who reported eating more than 5 servings of vegetables and fruit per day had approximately 41% lower risk of developing renal cell carcinoma when compared to women who reported eating less than a serving of vegetables and fruit per day. This result was not "statistically significant", which means it could have occurred due to chance or random error. However, in discussing the study, the researchers indicated that there are many reasons to believe that this finding is real. In other words, despite the lack of a "statistically significant" connection, the researchers felt that eating more vegetables and fruit did indeed lower the risk of renal cell cancer in this study.

Second, the researchers found that women who reported eating one or more servings of root vegetables per day had 51% lower risk of developing renal cell carcinoma when compared to the women who reported eating no root vegetables on a regular basis. For this study, root vegetables included carrots and beets. In other words, eating carrots and beets daily appeared to decrease risk of kidney cancer by 51% in this study. This result was statistically significant.

What do these results mean?

If the women in this study are like most people, then this study suggests that eating more than 5 servings of vegetables and fruit per day may decrease risk of the most common form of kidney cancer by up to 41%. In particular, eating one or more servings of root vegetables (carrots & beets) daily lowered the risk of this cancer the most. Eating carrots and beets daily lowered risk of renal cell carcinoma (kidney cancer) by over 50%. 

However, before we decide what these results mean, it is important to consider some of the limitations of this study.

First, this type of study cannot prove cause and effect; it only tells us that there is an association between certain dietary factors and risk of renal cell cancer. It is important to remember that an association is not causation (cause and effect).

Second, renal cell carcinoma is not a common cancer and because of this, it is hard to study. Only a very small number of women in this study developed this type of kidney cancer during the study period. This may explain why the result that eating more than five servings of vegetables and fruit per day was not "statistically significant". Often, it is easier to prove a "statistical" connection between a risk factor and a disease if the disease is more common in the general population.

As well, this study asked people about their diet at one point in time. This approach does not tell us anything about what a person's diet looked like throughout the study period or what his or her diet was like decades ago. Often, people change their eating habits over time. This may have an effect on their risk of disease. This research study did not account for changes in diet over time.

Finally, this study was conducted in Sweden. This means that the overall diet and lifestyle patterns of the people in this study may be different from people in other countries. For this reason, these results may not apply to people living outside of Sweden. However, research suggests that many health factors may be similar among people living in Sweden and people living in the United States and other developed countries (7,8).

On a positive note, the results of this study (6) do agree with much of the earlier research on diet and renal cell carcinoma. Several studies have come to the conclusion that vegetables and fruit may protect against this type of kidney cancer (9-13).

In summary, despite some weaknesses of the study reviewed (6), it fits well with what we know about diet and renal cell cancer risk. It adds another useful piece of information to the puzzle. More importantly, there are NO downsides to improving diet and eating healthy! In addition to lowering risk of renal cell cancer, these same foods (vegetables and fruit) reduce the risk of other cancers, heart disease, hypertension, and stroke, all of which are major killers in the United States (14-23). 

Eating To Reduce Risk Of Kidney Cancer

Before focusing on specific diet changes to reduce risk of renal cell cancer, be sure to address the known risk factors for this disease. Research consistently shows that two things will increase risk of renal cell cancer. Cigarette smoking and being overweight will increase the risk of this type of cancer.

Quit Smoking

If you smoke, talk to your doctor about making a plan for quitting. Quitting smoking is challenging, but you can succeed. Obtaining help from your medical care provider who can prescribe nicotine replacement therapy such as the patch, gum, nasal spray, or inhaler will substantially increase the chances that you quit for good (25). In addition to nicotine replacement, you can obtain advice from your doctor on support groups, "quit smoking" programs, and other ways to help yourself give up the smoking habit for good.

Maintain A Health Body Weight

If you are overweight, make it a priority to reach and maintain a healthy body weight.

Being overweight and obese is very common in the United States. Two-thirds of all adults in the United States are overweight or obese. This is nearly 70% of the adult population! However, this does not make it any less important to address this health problem right now in your own life.

Look at your current height and weight and be honest with yourself about whether you are overweight. This may be harder than it sounds! Researchers have found that many overweight and obese adults do not know that they are above a healthy body weight (26-28). The first step toward a healthy body weight is accepting where you are so that you can focus on how to manage your weight and improve your health.

Let go of self-blame and move onto self-care!!

Healthy Diet Changes

The research we reviewed here tells us that eating more vegetables and fruit may reduce the risk of renal cell cancer. In particular, eating 5 or more servings of these foods every day is an important goal. This may sound like a lot, but a serving may be smaller than you imagine.

A serving of fruit is:

• 1 medium apple, banana, or orange
• 1 melon wedge
• 1/4 to 1/2 cup berries or chopped fruit
• 1 to 2 oz dried fruit (a small handful)

A serving of vegetables is:

• 1 cup, loosely packed raw green leafy vegetables or 1/2 cup cooked greens
• 1/2 cup chopped any other vegetable, cooked
• A handful of baby carrots (5-7)
• 6 oz vegetable juice

Be sure to focus on root vegetables, in particular carrots and beets. The research reviewed here suggests that these foods are particularly important for lowering renal cell cancer risk.

• Try a Super Carotene Smoothie as an easy way to get more carrots into your diet.
• Try roasted root vegetables in your next meal. You can prepare these in the oven or on the grill.
  • To prepare root vegetables in the oven, Chop carrots, fresh beets, potatoes, sweet potatoes, parsnips, onions, and other root vegetables into 1/2 to 3/4 inch cubes. Toss lightly with a tablespoon of olive oil. Sprinkle with black pepper, rosemary, thyme, oregano, or any other spice that you like. Bake in a glass baking dish at 375°F for 50 to 60 minutes, or until vegetables are tender.
  • To prepare root vegetables on the grill: Chop carrots, fresh beets, potatoes, sweet potatoes, parsnips, onions, and other root vegetables into 1/2 to 3/4 inch cubes. Toss lightly with a tablespoon of olive oil. Sprinkle with black pepper, rosemary, thyme, oregano, or any other spice or combination of spices that you like. Wrap vegetables into small foil "packets". Place on the grill for 40 minutes, turning the packets over half way through cooking time. Be careful when unwrapping vegetables from foil - they will be very hot! As well, root vegetables can be placed on skewers and cooked as shish kabobs.

Getting Started

• When you are trying to improve your eating habits, the best place to start is with your attitude!
  • Eating healthy is not a punishment.
  • Eating healthy is a gift to yourself.
  • Eating healthy is not an all or nothing game. You can have a healthy diet and still enjoy 'treats' and 'fun' foods.
  • Start by making small manageable changes and build on your successes.
  • It may take several months to change you eating habits noticeably, but by gradually working on your diet now, you can make these healthy changes a permanent part of your commitment to better health.
  • Start your day right. Try a smoothie for breakfast. This can help you get several servings of fruit and vegetables into your diet first thing in the day.
  • Keep little 6 oz cans of low-sodium vegetable juice handy for a quick serving of vegetables.
• Rely on frozen vegetables and fruit during the off season. Generally, these are as nutritious as fresh.
• Add a handful of frozen blueberries, strawberries, or blackberries to your cereal.

NOTE: If you are in cancer treatment, these diet changes may not be right for you.

References

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2. Hu J, Ugnat AM; Canadian Cancer Registries Epidemiology Research Group. Active and passive smoking and risk of renal cell carcinoma in Canada.
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4. Murai M, Oya M. Renal cell carcinoma: etiology, incidence and epidemiology. Curr Opin Urol. 2004;14(4):229-33.

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6. Rashidkhani B, Lindblad P, Wolk A. Fruits, vegetables and risk of renal cell carcinoma: a prospective study of Swedish women. Int J Cancer. 2005;113(3):451-55.

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9. Yuan JM, Gago-Dominguez M, Castelao JE, Hankin JH, Ross RK, Yu MC. Cruciferous vegetables in relation to renal cell carcinoma. Int J Cancer. 1998;77(2):211-16.

10. Wolk A, Gridley G, Niwa S, Lindblad P, McCredie M, Mellemgaard A, Mandel JS, Wahrendorf J, McLaughlin JK, Adami HO. International renal cell cancer study. VII. Role of diet. Int J Cancer. 1996;65(1):67-73.

11. McLaughlin JK, Gao YT, Gao RN, Zheng W, Ji BT, Blot WJ, Fraumeni JF Jr. Risk factors for renal-cell cancer in Shanghai, China. Int J Cancer. 1992;52(4):562-65.

12. Negri E, La Vecchia C, Franceschi S, D'Avanzo B, Parazzini F. Vegetable and fruit consumption and cancer risk. Int J Cancer. 1991;48(3):350-54.

13. Maclure M, Willett W. A case-control study of diet and risk of renal adenocarcinoma. Epidemiology. 1990;1(6):430-40.

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Publish Date: 06/2005