This states the main conclusion. The doctor argues that taxing junk food would improve public health. The rest of the passage explains why taxing junk food would have this effect. Since unhealthy eating causes many health problems, taxing junk food would help reduce these issues.

This is a premise. The doctor claims that in many countries, including the doctor's, overeating junk food causes serious health problems. This supports the argument that making junk food more expensive would improve public health by reducing overeating and these related problems.

This is a premise. The doctor claims that if junk food were more expensive, people would eat healthier food, reducing health problems. This claim supports the doctor's main conclusion that taxing junk food would improve public health.

This is a premise. The claim that taxing junk food would make people eat less of it and more healthy food supports the doctor's argument that taxing junk food would improve public health by reducing the risk of health problems linked to eating too much junk food.

The doctor doesn’t make this claim. The doctor concludes that taxing junk food will have at least one positive effect—it will benefit public health—but doesn’t recommend that junk food should be taxed based on this effect. Other considerations may weigh against taxing junk food.