Looks like a derivation on the 5/2 diet. The 25/5 diet. My personal issue with these types of diets is that my concentration levels initially drop. I find the first couple of days extremely uncomfortable.
The best lifestyle change I've made is to drastically cut down on carbs, generally avoiding wheat and try never to eat sugar, in particular fructose. Note this doesn't stop me eating carbs but that I generally try and avoid them in my day to day eating. I no longer feel tired in the afternoon.
Not op - My experience is that all grains (corn, rice, wheat) make me bloated and puffy, regardless of caloric content. Wheat is by far the worst offender, also making my breath shorter about 30-60 minutes after eating, lasting a couple of hours, and corn not having an immediately noticeable effect, but causing bloating that will stay for days.
Not celiac, and not anything life threatening, but definitely a huge effect. After dropping wheat, I lost 30 lbs in one month, and it stayed off for 18 month without wheat (but some came on again after a week of eating mostly corn products - which is how I discovered that corn is evil too)
The best way to determine if this is relevant to you is not to read books or articles or consult with a doctor: rather, take a week or two off grains (much harder than it sounds - wheat and corn are used as fillers in many products), and then adding them sporadically and keeping a journal (what and when you ate each day; and whether you felt good/bad the next hour/day)
As some others have noted, white flour products and other high-carb, high glycemic-index foods tend to lead to hunger in the short term and lethargy ('food coma').
Anecdotally, I've noticed that if I eat a small breakfast high in protein - e.g. 3 eggs - then I don't get hungry for several hours. If I eat a large breakfast high in carbs - e.g. pancakes or waffles - then I am hungry much sooner.
1) If I eat a carb rich meal, I will happily go for a nap. Anecdotal evidence, had spaghetti carbonara with garlic bread at the weekend. Fell asleep watching a film for the first time in about a year. I can create the same effect with potato or rice. I don't like it. It wastes my time.
2) After eating a lot of bread I can feel extremely bloated and uncomfortable. I potentially have a gluten intolerance however I find the same when eating a lot of sugar. It could be yeast related. Through experimentation I've found that the white 'gacky' sliced bread is particularly bad.
3) I don't think we are designed to eat modern wheat. I switched from beer (ale) to cider and find I have no morning after 'bowel' effects.
4) I avoid sourdough bread. Who am I kidding. Best bread in the world. My crack cocaine. Thankfully there are some awesome artisan bakers in Bath, UK. However when I buy a loaf, I commit to a 20+ mile cycle ride.
5) If I eat a carb rich meal, I will get hungry quicker. I can feel 'fuller' for longer by avoiding carbs. It makes me avoid snacks.
A lot of the above is about feeling mentally alert at work/home. In the winter it means I cook up big pots of high protein stew, freeze them and take them to work and zap them in the microwave. Summer is all about big boxes of salads, heavy on the meat/cheese/dressing.
At work we have lunchtime Dirty Burger Wednesdays where we grab nasty takeaway food :) Like I said it's not about being religious about not eating wheat, just generally trying to minimise intake. I know what a high carb diet makes me feel like.
One proviso. I cycle to work. The morning is almost a free wheel 2.5 mile down hill ride. The evening is a 2.5 mile climb. It used to be a real bitch. Now only the last 0.5 mile is a bit nasty.
I eat some fruit in moderation, but avoid juices and carbonated drinks which use high-fructose corn syrup.
IIRC Fructose is processed in a similar way to the way alcohol is processed in your system. It's not an energy source that can be used by your body without processing. I also believe it's one of those energy types that is readily stored as fat.
I read that the liver is the only organ that can process fructose directly. I tried taking honey before bed in order to avoid hangover. Seemed to work, but may have been placebo effect.
The best lifestyle change I've made is to drastically cut down on carbs, generally avoiding wheat and try never to eat sugar, in particular fructose. Note this doesn't stop me eating carbs but that I generally try and avoid them in my day to day eating. I no longer feel tired in the afternoon.
I also cycle to work.