Publicity about a recent laboratory study has created quite a stir, suggesting that eating peanuts might help cancer cells to spread. However, a closer look at the study’s methods reveals some important reasons why we should interpret it cautiously. Laboratory research can provide important insights, but we should not leap to the conclusion that purified compounds in cultured cells and experimental mice will have the same impact in humans.
This is a perfect example of the well-known expression that sometimes “You can’t see the forest for the trees.”
It is important to consider how a study’s approach translates to human consumption, how the mechanisms studied fit with overall health and how the proposed conclusions fit with existing research in human populations.
Using this about peanuts as an example, here are three key questions you should ask when you see headlines that jump from a laboratory study to dietary recommendations or seemingly dire warnings.
How Does This Study Translate to Human Consumption?
In this study, the treatment of cells with a specific individual protein (peanut agglutinin, or PNA) triggered the release of two cytokines (signaling proteins in the body). These two cytokines have been linked to an increased ability for cancer cells to spread (metastasize) to other parts of the body.
Although the signaling pathways involved in this study are important in the cancer process, several important points seem to be overlooked in the panic-promoting headlines about the study.
- Dose provided: In all aspects of health—whether it’s about something that increases risk or something that offers protection—dose is a crucial part of results. In this case, PNA makes up 0.15% of peanuts’ weight, so the dose of the PNA protein used in the experiments was equivalent to what you would get from eating about 8 ounces (about 1 ½ cups) of peanuts!
Studies exploring cellular mechanisms often use high doses to make it easier to detect potential effects. But in many cases, the same substance at a lower dose does not exert an effect, and that may be the dose that’s relevant to human exposure.
- Body levels: And you’d need to eat all 8 ounces of peanuts at once, not spread throughout the day. The researchers have noted that levels of the PNA protein in this study only reached this level in the blood for about an hour after humans ate their half-pound of peanuts.
How Do Mechanisms Studied Here Fit in Overall Health?
The authors of this research paper added up the results of several individual experiments to conclude that the PNA protein from peanuts can trigger a signaling pathway that may lead to increased ability of cancer cells to spread.
Studies on how cancer-related cell signaling pathways can be increased or inhibited are tremendously valuable. But their role is in laying groundwork for expanding scientists’ understanding of mechanisms that can then be tested in further research that includes more pieces of the puzzle.
A food’s effects are the result of the thousands of nutrients and compounds it supplies—not just one.
For example, peanuts also contain resveratrol, a phytochemical that in laboratory studies increases the activity of antioxidant enzymes, inhibits ability of cancers to create new blood vessels needed to grow and inhibits the signaling pathway that the PNA protein seems to promote.
Like other nuts, peanuts also supply arginine, an amino acid that extensive studies show exerting healthful effects on blood vessel function. That’s highly relevant to people with cancer, since cardiovascular disease is a major cause of death after cancer.
How Do Results Fit in the Context of Human Studies?
The signaling pathway that this study highlights as central to the PNA protein’s effects is also intricately involved in growth, reproduction and survival of cancer cells. And the pathway is involved in resistance to chemotherapy, too.
Therefore, if this protein in peanuts has the potential to affect pathways promoting cancer metastasis that’s relevant to typical dietary choices, then we’d expect that greater peanut consumption would be linked with higher mortality rates. After all, cancer is by far one of the major causes of death in our country.
But that’s not what we see.
- In large population studies that follow people for 10 to 20 years, people who eat the most peanuts show either similar or lower mortality rates compared to people who eat the least amount of peanuts.
- In studies of men with prostate cancer, in the years after diagnosis, greater consumption of nuts (which in the U.S. is dominated by peanuts) is generally associated with fewer deaths during follow-up.
- Greater peanut consumption—and greater consumption of nuts overall—is strongly associated with lower risk of . And it doesn’t take half a pound a day! Just a few one-ounce servings a week is all it takes.
These are observational studies and don’t prove peanuts or nuts overall as a cause of better health. People who eat more nuts tend to have lots of healthy habits. They’re less likely to smoke and more likely to have a healthy weight and get regular physical activity. They tend to eat less red and processed meat and more vegetables and fruits than people who seldom eat nuts. But in studies that adjust for factors like this, nuts remain associated with lower mortality rates and better health.
Step Back and Look at the Big Picture on Healthy Eating
Laboratory studies play a crucial role in enhancing the understanding of factors involved in cancer development and progression.
But laboratory studies are not the place to turn to for ideas on how your eating choices can reduce your risk of cancer or improve cancer outcomes. There’s no reason to steer clear of a food based on theoretical risks when the benefits have been well documented.
Three Big Take-Aways:
>>How does a food fit in overall eating habits? Even looking beyond individual compounds in food to the food as a whole doesn’t tell the whole story. Are you simply adding a food to overall unhealthy eating habits? Or are you swapping peanuts and other nuts as replacements as part of reducing processed meats, sweets and excess portions of refined grains?
>>Food fears don’t help. Fixating on one possible implication of a laboratory study that’s not supported by studies in humans can result in a lot of unfounded fears. In my experience as a dietitian, a sense of panic is more likely to lead people to lose track of step-by-step tangible improvements they were making toward long-term healthy eating.
>>Focus your energy on food choices that have strong evidence supporting their value in promoting health. The AICR Third Expert Report and Continuous Update Project provide the strongest foundation for food choices related to cancer. Don’t get distracted by single headlines about individual studies. Just keep moving forward, aiming for progress, not perfection.