The cancers your body fat is most likely to affect

Higher body fat was linked to 19 of the 25 cancers. That's the number you'll see everywhere. But it's not the one to act on.

The one to act on is smaller. Nine of those links held up when researchers tested them with genetic data. Those are the ones that are most likely to be real, not just a pattern in the numbers.

Endometrial cancer had the largest increase. For every five points of BMI, risk was about 58% higher. If you're a woman in your 40s, 50s, or 60s, that's the one to take most seriously. The American Cancer Society's guide to endometrial cancer risk factors lays out the other factors that matter alongside weight.

Esophageal adenocarcinoma, a cancer of the lower esophagus, came next at about 47% higher. Kidney cancer followed at about 30% higher.

For context, five BMI points is roughly 34 pounds for someone who's 5'9". The National Cancer Institute's obesity and cancer fact sheet is a good overview if you want the basics before the detail.

Every number below is the increase in risk for each five-point rise in BMI.

When you test an observational link, you're asking whether two things move together. Genetic data asks a sharper question: does a genetic predisposition to higher BMI also come with a higher cancer risk? If yes, the link is much harder to dismiss.

Nine passed. The strongest were esophageal adenocarcinoma and endometrial, followed by gallbladder and kidney. Liver, pancreatic, meningioma, and colorectal also held up.

That's the shortlist that matters. These are the cancers where the body fat link is most likely to be real.

Three cancers showed lower risk with higher BMI. Premenopausal breast cancer came in about 8% lower. Lung cancer in never-smokers was about 8% lower. Esophageal squamous cell cancer in never-smokers was about 28% lower.

These are the findings I'd treat with caution. They run against the general picture, and many of the studies behind them come from a limited set of populations. They're interesting, but they aren't permission to think differently about body fat.

Waist size and BMI gave similar results overall. The detail is more useful.

Colorectal and gastric cardia cancers were linked to both measures. Esophageal squamous cell cancer went the other way for both, and lung cancer was linked to BMI only.

In practice, a waist measurement gives you roughly the same information as BMI for most of these cancers. It's cheaper to check, and it doesn't mistake muscle for fat, which matters if you lift.

Most of the genetic data came from people of European ancestry. Many world regions weren't represented. Most cohorts were healthier and wealthier than the general population. And rarer cancers and subtypes weren't analyzed at all.

So this is a strong signal for some cancers in some populations. It isn't a complete map for everyone

1. Know your numbers. Measure your waist once a month and track the trend over three months. Keep your height and weight so you can see your BMI over time.

2. Take symptoms seriously. Unexplained bleeding, changes in bowel habits, blood in your stool, or persistent pain go to your doctor. Don't wait for a trend line to tell you something's wrong.

3. Use the screening you're offered. October is Breast Cancer Awareness Month, so if you're due a mammogram, book it. Colorectal screening now starts at 45 for average-risk adults, according to the US Preventive Services Task Force, and cervical screening has set schedules too. Ask your doctor which tests you need and when. Screening catches changes early, which matters more than any single lifestyle choice.

Weight and waist are part of the picture. They're not the whole story. But they're the part you can influence this week.

So this week, measure your waist and write it down. Then check whether you're due for any screening you've been putting off.

Adiposity and cancer: systematic review and meta-analysis, Nature Metabolism - The full paper, including the per-cancer figures and the genetic analysis.

Lifetime obesity exposure in cancer patients is widely underestimated, University of Oxford - Why how long you've carried excess weight may matter more than what you weigh today.