Ok let’s be clear, you cannot be “keto” if you eat low carbs/high fat 2-3 days per week (especially on non-consecutive days like it would happen in your question).
KETO refers to becoming adapted to using ketones as the primary fuel source. For that to happen you need to be in a physiological state where very little glucose (carbs) are available. This means almost no carbs in the diet and very little glycogen stored in the muscles and liver. If there is plenty of glycogen (stored glucose) in the muscles and liver you will not adapt to using ketones as your primary fuel source.
If you go “keto” for 1 or even 2 days you will not deplete muscle and liver glycogen (especially in your example where the keto days are on non-training days).so even if you eat no carbs for 1-2 days you will not become keto adapted. But even if you were, you would drop right out of that state by having carbs for the next few days.
Not only do you need to have no significant amount of glucose available for fuel, you must be in that state for a fairly long period before you become “keto adapted”. Most keto experts talk about being in that state for at least 3 weeks to become fully keto adapted.
So as you can see just because you have 2-3 days of low carbs/high fat in your week doesn’t qualify as “keto”… a lot of people just like to fall in love with a concept and attach the keto work to it.
That having been said I’m not saying that the approach will not work. It will work, but not because it’s “keto”… simply because a few days a week you are consuming a caloric deficit and and energy deficit. Having days with lowered calories will indeed limit fat gain when you are eating a surplus on the other days. I call these “control days”.
They only work bey reducing the average caloric intake over the week.
Let’s say that your maintenance level is 2500 calories per day and that you are 200lbs; so you need 200-250g of protein per day (800-1000 calories)…
Let’s say that on your “gaining” days you consume 3200 calories with 250g of protein , 300g of carbs (1200 calories) and 110g of fat (1000 calories). And you have 5 such days in a week.
On the other two days you also ingest 250g of protein (1000 calories) but only 1700 total calories. It gives you 500 “energetic” calories (fats or carbs). It absolutely will not matter if those 700 calories come from carbs, fats or a mix of both… you could eat…
152g of carbs and 10g of fats
88g of carbs and 39g of fats
50g of carbs and 56g of fats
25g of carbs and 67g of fats
0g of carbs and 78g of fats
And in the long term it will make zero difference in body composition. All options will be effective to the same extent.
In that case it would give you a weekly caloric intake of 19400 calories or an average of 2771 calories/day, which in the example is a surplus of a bit more than 250 calories per day along with enough protein to support growth. For someone with a 2500 calories maintenance level this would allow for a gradual gain in muscle mass and basically no fat gain.
