▲你的句子结构有问题，在网上查了一下，你的句子漏了一个so，即：

They find that they feel so much better that it reconstructs the reason for making these changes from fear of dying to joy of living.

▲注意添加的这个so与后面的that构成so…that…句式，意思是“如此……以致”，即“人们感觉如此的好以致……”；that 从句中的主语 it 用于指代 they feel so much better 这件事；from fear of dying to joy of living 其实是一个 from…to…结构，意思是“从害怕死亡（转变）到享受生活”；reconstruct 的意思是“重建”“重构”“再现”“修复”等，此处的 reconstructs the reason 可理解为“重新解释”。句子意为：他们发现，他们感觉好多了，这也解释了人们要作出改变的原因——从原来的害怕死亡到现在的享受生活。

▲附原文如下，供参考：

Life is to be enjoyed. There’s no point in giving up something you enjoy unless you get something back that’s even better. When people eat more healthfully, exercise, quit smoking, and manage stress better, they find that they feel so much better that it reconstructs the reason for making these changes from fear of dying to joy of living. The latest studies show that when you exercise and eat right:

YOUR BRAIN receives more blood flow and oxygen, so you become smarter, think more clearly, have more energy, and need less sleep. Two studies showed that just walking for three hours per week for only three months caused so many new neurons (神经细胞) to grow that it actually increased the size of people’s brains!

YOUR FACE receives more blood flow, so your skin glows more and wrinkles less. You look younger and more attractive. In contrast, an unhealthy diet, chronic emotional stress and smoking reduce blood flow to your face so you age more quickly. Smoking accelerates aging because nicotine causes your arteries (动脉) to narrow down, which decreases blood flow to your face and makes it wrinkle earlier. This is why smokers look years older than they really are.

YOUR GENES change. In May, a study was published in the Proceedings of the National Academy of Sciences showing that changing your lifestyle changes your genes.

YOUR TELOMERES (染色体端粒) get longer. Telomeres are the ends of our chromosomes (染色体) that control how long we live. As telomeres become shorter, then cells age more quickly, thus shortening your life.

 Besides, one of the most interesting findings in the study was that the mothers’ awareness of stress was more important than what was really occurring in their lives. The researchers gave the women a questionnaire and asked them to rate on a three-point scale how stressed they felt each day, and how out of control their lives felt to them. The women who were aware that they were under heavy stress had significantly shortened and damaged telomeres compared with those who felt more relaxed. On the contrary, some of the women who felt relaxed despite raising a disabled child had more normal-appearing telomeres.

In other words, if you feel stressed, you are stressed; if you feel fine, you are fine.