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WCRF/AICR
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Frequently Asked Questions

During Treatment

Below are answers to some of the most common questions about diet and exercise for cancer patients undergoing treatment.
If you have recently completed or are currently in treatment, please ask your doctor or registered dietitian for specific dietary and activity guidelines.

Why am I so tired? What can I eat to boost my energy?

Fatigue is one of the common symptoms among cancer patients and survivors and researchers still do not fully understand its causes. Changes in nutrition can affect fatigue and yet feeling fatigued can also make it more challenging to eat healthy. You should discuss the problem with your physician.

In the meantime, eat for good health. A plant-based diet that includes enough calories to support a healthy weight and meet any increased nutritional requirements is ideal. Protein (animal or plant) or whole grains tend to provide more sustained energy than refined carbohydrates.

You should also drink plenty of fluids. Dehydration worsens fatigue. Make sure you drink at least 8 cups a day. If you are gaining too much weight, drink mostly water; if you are unintentionally losing weight; include some calorie-providing fluids such as milk or juice.

Exercise, especially a light to moderate walking program, can also help lessen fatigue and improve your sense of well-being. Your physician can offer guidance concerning when to start physical activity and how much activity is right for you.

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Should I take antioxidants or other supplements?

If you are still undergoing cancer treatment, discuss supplementation with your physician. Several recent population studies suggest that antioxidant supplements may interfere with cancer treatment, yet the research is not conclusive. Theoretically, the same mechanisms that antioxidant supplements use to protect healthy cells from cancer may also protect the cancer cells during treatment.

If you have completed cancer therapy, it is important to know that supplements cannot replace a varied and healthful diet. Many individuals can benefit from adding a “one-a-day vitamin pill” that offers a 100 percent Daily Value (DV) of vitamins and minerals.

But you cannot obtain the protective benefits linked to eating a wide variety of plant-based foods such as vegetables and fruits by isolating specific substances into pills. Researchers have not yet identified all the protective phytochemicals in fruits and vegetables, and studies suggest that phytochemicals in foods work together to provide cancer protection and other health benefits. In addition, a balanced diet provides fiber, protein and essential fatty acids necessary for health.

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Should I switch to a low-fat diet?

Optimal amount of dietary fat varies among individuals. During treatment, you should focus on eating healthful foods that your body can handle. Some types of cancer and their treatment may lead to problems digesting dietary fat, leading to a specific type of diarrhea that improves with a low-fat diet. Other people, however, have trouble taking in enough calories, and if fat digestion is not a problem, dietary fat can be an important source of concentrated calories.

Although dietary fat was once considered a major factor in cancer risk, research has shifted focus to emphasize the cancer-protective effect of vegetables and fruits. After treatment, for better general health, you should avoid excessive amounts of fat, especially saturated fat, which is found in fatty meat and high-fat cheese, milk and ice cream. But some fat is needed in your diet. Moderate amounts of olive and canola oils, nuts and fatty fish are good choices.

Should I become a vegetarian?

Both during and after cancer treatment, there is no reason to switch to a vegetarian diet.

For cancer survivors, research shows that the most important dietary change you can make is to stay a healthy weight, eat a plant-based diet, and exercise for 30 minutes daily. It does not appear that vegetarian diets are any more protective than other mostly plant-based regimens. AICR recommends that you fill your plate with two-thirds (or more) vegetables, fruits, whole grains and beans and one-third (or less) fish, poultry or meat.

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During and after my treatment, should I eat flaxseed?

Flaxseed, like soy, seems to have relatively weak estrogenic effects in the body. Research involving flaxseed has focused on breast and prostate cancers. More research on flaxseed is needed to make a specific recommendation. Talk to your doctor.

After cancer treatment, studies suggest that a small amount of flaxseed can be a part of a healthy diet. In laboratory studies, flaxseed has shown anticancer properties but these studies are inconsistent. For now, a small amount of ground flaxseed (1 tablespoon) per day seems safe and may provide some general heart health benefits because of its omega-3 fat and fiber.

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Does sugar promote cancer? Should I avoid it?

Sugar alone does not promote cancer. Consuming small amounts of sugar as part of an overall healthful diet is fine, but large amounts of sugar may indirectly raise cancer risk in two ways.

First, diets high in sugar may lead to elevated blood sugar levels, which can raise insulin levels. Routinely high levels of insulin may, in turn, increase the risk of colon cancer, and perhaps other cancers. This indirect chain of events is seen most commonly among people who are overweight and sedentary or those who have insulin resistance or diabetes in the family.

Another way high sugar consumption may increase cancer risk is by leading to weight gain. High sugar foods are typically high in calories and over time a high calorie diet leads to excess weight. And excess weight is linked to greater risk of several types of cancers.

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Which fruits and vegetables should I be eating?

Eat as many different vegetables and fruits as you can. Variety is the key to obtaining the many protective phytochemicals in plant-based foods. Each vegetable and fruit has its own profile of health-promoting substances.

The phytochemicals found in cantaloupe are different from those in broccoli or leeks or cherries. Try to include a lot of colors on your plate. Aim to eat some bright red, green, orange, blue, purple and yellow vegetables and fruits each day.

Should I buy organic foods whenever possible?

Currently, there is no convincing evidence that shows a difference between organic and conventionally grown foods related to cancer risk. Market studies show pesticide residues on conventionally grown foods are almost always within safety tolerance limits.

If you are concerned about pesticide residues and can afford to spend more, organic produce may be a choice for you as long as the higher cost will not lead you to cut back on eating fruits and vegetables.

Eating generous servings of a large variety of veggies and fruits - whether organic or not will be beneficial to your health. The advantages of including more vegetables and fruits in your diet strongly outweigh any potential risks from pesticides.

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