Weight, Alcohol, and Food

Two things are established. A lot is not.

This is the noisiest topic in cancer. Every week, some food is said to cause cancer or cure it.

So it helps to know where federal agencies plant their feet. NCI's own summary of diet research is worth reading twice. With few exceptions, it says, studies of human populations have not yet shown that any part of the diet clearly causes or prevents cancer.

Alcohol is one of those few exceptions. Body weight is the other big one. Start there.

Alcohol

NCI treats alcohol as a known cause of cancer.

The Surgeon General's advisory on alcohol and cancer names seven cancers with a proven causal link:

• Breast, in women
• Colon and rectum
• Esophagus
• Liver
• Mouth
• Throat
• Voice box

CDC's list is the same. The advisory adds a count. About 96,730 US cancer cases in 2019 were linked to alcohol. And about 20,000 alcohol-related cancer deaths happen each year.

Two details surprise people. First, about 17 percent of those deaths happen at drinking levels already inside the US Dietary Guidelines limits. Second, less than half of Americans know that alcohol raises cancer risk at all.

NCI adds that even light drinkers can be at higher risk of some cancers. For breast cancer, NCI reports risk about 1.04 times higher with light drinking. With moderate drinking it is about 1.23 times higher. For mouth cancer, heavy drinking is linked to about five times the risk.

NCI is also clear about the limits. It calls the link to melanoma possible but not proven. The same goes for cancers of the pancreas, prostate, and stomach. For bladder, ovarian, and uterine cancer, NCI says the evidence is mixed.

On limits. CDC cites the 2020-2025 Dietary Guidelines. Adults of legal drinking age should either not drink, or drink in moderation. That means two drinks or less a day for men, and one drink or less for women. CDC adds that even moderate drinking may carry health risks. These guidelines are revised from time to time, so check the current edition before treating a number as final.

Body weight

A large review looked at more than 1,000 studies. It found steady evidence that more body fat goes with higher risk of a number of cancers.

The two biggest links NCI reports:

• Cancer of the uterus lining: about seven times the risk with severe obesity, and about two to four times with excess weight
• One kind of cancer of the esophagus: about five times the risk with severe obesity

NCI lists smaller rises, from about 10 percent up to double, for cancer of the colon, kidney, liver, pancreas, ovary, thyroid, gallbladder, upper stomach, and breast after menopause. Two others are on the list: multiple myeloma and meningioma.

NCI also puts a count on it for 2019, in people aged 30 and over. Excess body weight was behind about 43,720 new cancers in men, or 4.8 percent of them. In women it was about 92,200, or 10.6 percent.

Moving

NCI reports strong evidence that the most active people have lower risk of several cancers than the least active:

• Colon: 19 percent lower
• Uterus lining: 20 percent lower
• Esophagus, one kind: 21 percent lower
• Stomach: 19 percent lower
• Breast: 12 to 21 percent lower
• Bladder: 15 percent lower
• Kidney: 12 percent lower

For other cancers the evidence is weaker. NCI calls it limited for lung, pancreas, prostate, ovary, thyroid, liver, rectum, and blood cancers. For lung, NCI warns the link may just reflect who smokes.

Food, honestly

Here is where the federal evidence will disappoint some expectations.

Cooking meat at high heat forms two kinds of chemicals. NCI says those chemicals damage DNA in the lab. But NCI also says that studies in people have not shown a clear link between them and cancer in humans.

The lab doses were huge. Rats got the equivalent of thousands of times what a person eats. Some human studies do link well-done or grilled meat to higher risk of cancer of the colon, pancreas, or prostate. Others found no link at all.

You may have seen an international agency rank processed meat differently. That ranking exists. But it is not what NCI or CDC say, and we will not put their name on it.

What is left is less dramatic and more useful than a list of banned foods. Alcohol and body weight are where the solid evidence sits. Both are worth raising with a clinician, for reasons well beyond cancer.