The concept
Nutra is the name given to the segment of health, supplement, weight-loss, and wellness product sales, common in affiliate operations selling to the United States and Europe. Nutra's average order value tends to be higher than that of digital products, and the operation faces country-specific regulation, such as FDA rules in the United States.
Because it deals with health products and has a higher chargeback history in the market overall, Nutra accounts tend to go through stricter risk review at payment platforms.
How it shows up in practice
You're an affiliate selling a weight loss supplement to people in the United States and Europe. The average ticket is high, the product works and people come back buying more. But the acquirer wants more documentation, more risk analysis and keeps asking for proof that the product really works and that the advertising matches local laws. All of this because Nutra is seen as a higher risk category at payment platforms.
The aim of marketing is to know and understand the customer so well the product or service fits him and sells itself.
You need to be prepared for this stricter analysis and have all product documentation on hand: composition, certificates, regulation for each country where you sell. A Nutra operation without this documentation can't even go live, because platforms want to ensure they're facilitating a legitimate sale and not a scam.