"Four horsemen of the apocalypse", what does it mean?
" If we truly wish to impact obesity, we need to explain that inactivity and sedentary behavior are two of the four horsemen of the apocalypse during pregnancy (alcohol and smoking being the other two); and the effect of these behaviors last a lifetime."
Note: The article was discussing the fact that inactivity during pregnancy might affect the embryo.
This is a Christian reference to the Book of Revelation. The four horsemen there are Conquest, War, Famine, and Death, and believed to begin the end of the world.
So for this context, the author is using strong imagery to group together four things pregnant women should avoid.