Researchers studied over 108,000 women to see how diet affects cancer risk, but they faced a common problem: people aren’t always accurate when reporting what they eat. Scientists used blood and urine tests to create a more accurate picture of women’s actual eating patterns. They found that women who followed healthier eating patterns had lower risks of lung cancer and overall cancer. The study suggests that when researchers account for reporting errors, the connection between healthy eating and cancer prevention becomes even stronger than previous studies showed.

The Quick Take

  • What they studied: Whether eating a healthier diet reduces the risk of getting cancer in women, using a more accurate way to measure what people actually eat
  • Who participated: 108,522 women from the Women’s Health Initiative study, followed for an average of 15.8 years (about 16 years)
  • Key finding: Women who ate according to healthy eating guidelines had a 21% lower risk of lung cancer and a 4% lower risk of all cancers combined when researchers used blood and urine tests to verify their actual eating patterns
  • What it means for you: Eating a healthy diet appears to help protect against cancer, especially lung cancer. However, this is observational research showing a connection, not proof that diet alone prevents cancer. Talk to your doctor about your personal cancer risk factors.

The Research Details

This study used a clever approach to solve a real problem in nutrition research. Normally, scientists ask people to remember and report what they ate, but people often forget or aren’t accurate. Instead, researchers created a special test using blood and urine samples that shows what people actually ate. They first tested this method on 153 women in a controlled feeding study where they knew exactly what the women ate. Then they used what they learned to analyze data from 450 women in an observation study, and finally applied it to over 108,000 women in the main study. Women were followed for about 16 years to see who developed cancer.

The researchers looked at two different healthy eating patterns: the Healthy Eating Index (HEI) and the Alternative Healthy Eating Index (AHEI). Both measure how well someone follows nutrition guidelines. The key innovation was using metabolites—tiny chemical markers in blood and urine—to verify whether people’s reported diets matched their actual eating patterns. This is like having a biological fingerprint of someone’s diet.

The study examined cancer risk using statistical methods that account for many other factors that might affect cancer development, like age, smoking, and exercise.

Most diet and health studies rely on people remembering what they ate, which introduces errors. These errors can make real diet-cancer connections appear weaker than they actually are. By using biological markers, this study provides a more accurate picture of how diet truly affects cancer risk. This matters because it helps doctors and public health officials give better advice about preventing cancer through diet.

This is a large, well-designed study published in a respected epidemiology journal. The researchers validated their method in a controlled feeding study before applying it to the larger population. The study followed women for over 15 years, which is long enough to see cancer development. However, the study is observational, meaning it shows associations but cannot prove that diet directly causes cancer prevention. The biological markers explained 48-62% of the variation in diet quality, which is good but not perfect.

What the Results Show

When researchers used the traditional method of asking women about their diets, they found that a 20% improvement in diet quality was associated with lower risks of colorectal cancer (6% lower), lung cancer (10% lower), bladder cancer (14% lower), and all cancers combined (2% lower). However, when they used the more accurate blood and urine test method, the results were even stronger for some cancers.

With the biological marker method, a 20% improvement in diet quality was associated with a 21% lower risk of lung cancer—more than double the effect seen with self-reported diet. The overall cancer risk reduction remained similar at 4% lower. This suggests that the true protective effect of healthy eating may be stronger than previous studies showed because the biological markers are more accurate.

The study found that the Alternative Healthy Eating Index (which emphasizes whole grains, fish, and nuts while limiting red meat and refined carbohydrates) performed similarly to the standard Healthy Eating Index in predicting cancer risk. Both dietary patterns showed protective effects, suggesting that multiple approaches to healthy eating can help reduce cancer risk.

The study found that different types of cancer responded differently to diet quality. Lung cancer showed the strongest protective effect from healthy eating. Colorectal and bladder cancers also showed associations with diet, though these were somewhat weaker. The researchers noted that the biological marker method was particularly effective at detecting diet-cancer relationships that might be missed when relying solely on what people report eating.

Previous research has suggested that diet affects cancer risk, but results have been inconsistent partly because of measurement errors in diet reporting. This study strengthens earlier findings by using a more accurate method. The lung cancer findings are particularly notable because they show a stronger protective effect than most previous studies reported. The overall cancer findings align with major health organizations’ recommendations that healthy eating patterns reduce cancer risk.

The study is observational, meaning it shows that healthy eating is associated with lower cancer risk, but cannot prove that diet directly prevents cancer. Other lifestyle factors not fully measured could explain some results. The study included mostly older women, so results may not apply equally to younger women or men. The biological marker method, while more accurate than self-reporting, still only explained about half of the variation in diet quality, meaning some measurement error remains. The study cannot determine which specific foods or nutrients are most protective.

The Bottom Line

Eat according to healthy eating guidelines that emphasize vegetables, fruits, whole grains, fish, and nuts while limiting red meat, processed foods, and refined carbohydrates. This appears to reduce cancer risk, particularly lung cancer risk. Confidence level: Moderate. This is based on a large, well-designed study, but observational studies cannot prove cause-and-effect relationships.

Everyone should care about this research, especially women and anyone concerned about cancer prevention. This is particularly relevant for people with family histories of cancer or those with known risk factors. However, diet is just one factor affecting cancer risk—smoking, alcohol use, physical activity, weight, and genetics also matter significantly.

Cancer develops over many years, so the protective effects of healthy eating take time to appear. The women in this study were followed for about 16 years before researchers saw clear differences in cancer rates. You should think of healthy eating as a long-term investment in your health rather than expecting immediate results.

Want to Apply This Research?

  • Track your daily servings of vegetables, fruits, whole grains, and fish. Aim for at least 2-3 servings of vegetables, 1-2 servings of fruit, 3-4 servings of whole grains, and 2-3 servings of fish per week. Use the app to log these foods and monitor your progress toward healthy eating guidelines.
  • Replace one processed food or red meat meal per week with a plant-based meal containing vegetables, whole grains, and legumes. Use the app to plan these meals and track when you complete them. Gradually increase the frequency as it becomes a habit.
  • Review your diet quality score weekly in the app. Compare your eating patterns to the Healthy Eating Index guidelines monthly. Track any changes in energy levels and overall health markers. Share reports with your healthcare provider during annual checkups to discuss how your diet may affect your personal cancer risk.

This research shows an association between healthy eating patterns and lower cancer risk, but cannot prove that diet alone prevents cancer. Cancer risk is influenced by many factors including genetics, smoking, alcohol use, physical activity, weight, and age. This information should not replace personalized medical advice from your doctor. If you have concerns about cancer risk or are making significant dietary changes, consult with your healthcare provider or a registered dietitian. This study was conducted in women and may not apply equally to men or younger populations.