Now we have variables like diet (fiber, fat, and protein), exercise (vo2 max), the exact date of intervention (just before and after), BMI, and metabolite data.
Our specific objective was to control for BMI and intervention time to find metabolite changes caused by exercise, metabolite changes caused by diet, and metabolite changes caused by exercise + diet, respectively.
We are familiar with lmer package and other tools in R, but we do not know how to design the model(Which variables shall be fixed effect, random effect? How to detect metabolites only associate with exercise and diet fiber?)
Our aim was to identify the effects of exercise and dietary fiber, as well as the effects of exercise + dietary fiber intervention on human metabolites. If you can list the illustrative models, it will help us so much! Thank you for your attention.