I recently changed my diet because I felt my energy levels were all over the place. I cut out processed carbs, and generally things with a high glycemic index. It took about three weeks to really get past sugary foods, but then my tastes started to change. I'm pescetarian (mostly vegetarian, occasional I'll eat fish), so protein is a challenge – I rely pretty heavily on eggs and yogurt. I also cut down on the amount of dairy I was consuming in general, switching to a macchiato for my afternoon coffee rather than a latte. Other than that, lots of vegetables in lots of variety.

Data point of one, but after a month I really started to feel a difference. I felt a lot better almost immediately, but some of that was likely placebo. I crash a lot less in the afternoons, and have higher energy in general. Physically the difference was more dramatic – lost a spare tire I was starting to cary around my mid section. Partially this was due to exercise – more energy led to commuting by bike a lot more than I was.

One thing I'd add to the article was the importance of changing your environment. When I first started it was difficult because most of the snacks at home were carbohydrate based – by changing the environment and stocking a lot more protein-based foods at home that were easy to prepare, it was a lot easier to make the transition.