What's the meaning of "radical" in this context?

Question

I came across the word in this passage of an article on a medical discovery:

Part of the reason that heart disease is so prevalent and intractable is that it often requires massive changes to one’s lifestyle— changes that are not easy to make. Everything from radically altering ones diet to implementing serious exercise routines. And while it’s never too late to start, people often realize the true danger only when it’s too late to make the changes and the damage is done.

This is the definition of radical from OALD:

1 concerning the most basic and important parts of something; thorough and complete

radically altering one's diet. I understand the latter part of the definition thorough and complete when it applies to diet, but what about the former part concerning the most basic and important parts of something? When it involves diet does it mean the three main meals?

Answer 1

The most common meaning of "radical" is extreme, calling for fundamental change. When the definition you quote talks about "the most basic and important parts of something", what they probably mean is CHANGING the most basic and important parts of something. If you've been eating 60% beef and 40% chicken and the doctor tells you that you need to eat 40% beef and 60% chicken, this would be a minor adjustment to your diet. He's not telling you to change the essentials, just the proportions. Or if he told you that you need to switch from chicken to turkey, again, the basic idea is the same, it's just the details that differ. But if he said you need to give up the beef and chicken entirely and starting eating only rice and vegetables, this would be a "radical" change to your diet. You are changing it at a fundamental level, not just surface details.