Many Nigerians who react badly to milk respond by cutting dairy out of their diet completely, when the part causing the trouble is a single sugar that some dairy foods carry far less of than others.
That sugar is lactose, and the body breaks it down with an enzyme called lactase.
Babies produce plenty of lactase because milk is the only food they have, but for most adults production falls away after childhood and never returns.
The National Institute of Diabetes and Digestive and Kidney Diseases reports that most people in Africa and Asia have lactose malabsorption, and that it is least common among people whose families come from Europe.
The condition is therefore common in Nigeria, and often mistaken for something else.
When lactase runs short, undigested lactose travels down to the large intestine, where gut bacteria break it down instead. That process is what produces the bloating, cramping and gas an hour after a glass of milk, a bowl of ice cream, or tea taken with plenty of milk.
The pattern has been documented in Nigerian families for half a century. A 1975 study published in Gastroenterology traced lactose digestion through family pedigrees and found that where both parents could not digest lactose, none of their children could either.
This is a normal developmental pattern rather than an allergy.
Yogurt is handled differently by the gut. It begins as milk, but fermentation alters it before it reaches the chiller.
The live cultures in yogurt consume part of the lactose during fermentation, which is why plain yogurt carries less of it than the milk it was made from.
Those cultures also keep working during digestion. The European Food Safety Authority accepts that live cultures in yogurt improve digestion of the lactose in the yogurt, which is why many people who cannot manage a glass of milk handle a bowl of yogurt without trouble.
Lactose is only part of the picture, since how Greek yogurt affects digestion and gut health also depends on what those cultures do once they reach the intestine.
Greek yogurt adds one more step. The watery portion of the yogurt, called whey, is strained out.
Lactose dissolves in water, so a good share of it drains away with the whey. Straining also thickens the product and concentrates the protein, which is why Greek yogurt is the denser, heavier item on the shelf.
USDA FoodData Central lists about 4.8 grams of lactose per 100 grams of whole milk, and plain yogurt made from it comes in lower, with a strained Greek product lower again.
The exact figure varies by brand and by how long the yogurt has been strained, but the direction is consistent. A serving of Greek yogurt carries less lactose than the same serving of regular yogurt, which in turn carries less than the milk both came from.
Fermentation removes some of the lactose, and straining removes more.
Tolerance is personal, so it is worth testing your own rather than relying on an average.
Start with a small portion, two or three tablespoons, eaten alongside other food rather than on an empty stomach.
Choose plain unsweetened yogurt for the test. Added sugar and fruit flavouring do not change the lactose content, but they do make it harder to tell what you are reacting to.
Wait a few hours and note how you feel. A written record helps, because a reaction is easy to misremember a day later. If nothing happens, try a slightly larger portion the next day, and build up gradually across a week.
Many people who cannot drink milk at all find they manage yogurt comfortably at ordinary portion sizes, and knowing roughly where your own ceiling sits is more useful than avoiding dairy altogether.
One thing is worth ruling out before any of that. A milk allergy is a different condition from lactose intolerance, and the two are regularly confused.
An allergy involves the immune system rather than a missing enzyme. It can cause hives, swelling or difficulty breathing, and it does not improve with yogurt or with straining.
Anyone whose symptoms come on quickly or severely after any dairy at all should stop testing on their own and see a doctor. That is a different condition, and it needs a diagnosis rather than a change of product.
Lactose intolerance is uncomfortable, but it is manageable, and it rarely requires giving up dairy entirely.