For someone who is overweight, is eating semi-paleo still better than eating full-on SAD? By "semi-paleo" I mean paleo for most meals, but with a sandwich, some kind of sugary snack, or some other non-paleo fare about once a day or every other day.
The way I see it, there are two main possibilities:
Any paleo is better than no paleo, so even paleo with regular cheats are better than SAD, if most of your meals are paleo.
Keeping regular grains, carbs, and sugars in the diet (even if at a reduced amount) combine with the increased fat in a paleo diet to make bad things happen.
Which of those two is more correct, or is there another more-likely possibility I'm missing?
it depends -- i'd tend to agree the some paleo is better than none, but you should be aware that if you're eating some grains every day, and then using paleo as an "excuse" to eating a lot of high-fat foods, you may actually end up increasing your weight.
Number one. The further away you get from the SAD, the more benefit you will attain from eating paleo. However, it's the law of diminishing returns. Someone who is 90% paleo and goes 100% (regardless of your version of paleo) will reap less benefit than the person going from 50% to 60%.
Yes, of course, eating semi-paleo is going to be better. If you're doing paleo except for an excursion every day or two then you're on your way. The more real food you get into your body the better off you are. Even if there were some unpleasant effect of combining grains with more fat than you're used to eating you know that that's a transitional thing which will go away the more real food and the less grains you eat.
Some people switch to paleo cold turkey, others ease into it. I imagine the "easing into it" approach is more common. Whatever works for you is good.