To put it simply, is it processed/refined or whole/natural?
I don't think I need to say which is better than which.
There are a few reasons as to why.
1) Whole/natural food have nutrients that we need, other than just carb or fat or protein.
2) With processed/refined food, there is no or little need for the body to work to break down the food into the particles it needs to use and build up our body, so it just uses without spending much energy. With whole/natural food, our body uses energy in breaking down the food into particles that we need for energy, maintain health, and build up our body.
2) The process of breaking down and then rebuilding into what we need in itself is very good for maintaining our health. We need to keep the machine running, in order for the machine to run smoothly at all times.
As for the carbs. The minimum recommended intake is 130g per day, as our brains use only glucose as the energy sourse, except in emergencies. That's why you get brain fog with very low or almost no carb intake. You are starving your brain cells. A very special feature of glucose and brain cells is that unlike other cells, brain cells do not need insulin to use glucose. Now, the 130g is in wholesome carbs, so part of that will be spent in breaking themselves down, and what your brain needs in terms of glucose, of course, will be somewhat less. However, in terms of glucose level in the blood for the safety of your brain, the level should be kept at more than 50g/dl. In other words, you need to keep your carb intake at the level where your blood glucose level will stay at over 50g/dl at all times.
The same goes with lipids (fat). You need a certain amount of "good" fat to build your body. As with glucose, the reference level is the recommended range (which most people think of as normal range) and the respective lipids should be kept within that.
Just about all natural produce (in this case meaning veggies, crops, meat, fish, poultry, fruits, etc) include all three of the major nutrients, carb, fat, protein to some degree. When we medically describe a produce as being carb or fat or protein, means that the largest amount of nutrient (other than water) that is included is just that. For instance, raw white rice is about 70% or so carb, but it also has water, fat, and even protein, though just under 1%.
With meats, the range of protein is 18-23% or so protein, 5-35% fat, depending on which portion the meat is, some carbs (if I remember correctly, I think it was around 5%) and the rest, water. In other words, with a lot of produce, not just veggies, the major content is water, rather than carb, protein or fat.
For the break down in distribution of nutrients in daily intake.
The standard recommended range is
Of the total daily calories,
45-65% from carbs
10-35% from protein
20-35% from fat.
As I said, this is the standard range.
With bypass patients, you need to concentrate on the protein first, so it should be around 35% of total calorie intake, and the remaining 65% from carbs and fat, so, both of these nutrients will fall into the lower end of the recommended range. Which is fine, as even with a 1000kcal diet, protein intake at 35% amounts to 87g.
Hope this answers your Q.
Low Carb vs. No Carb 
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So long as you are putting your best foot forward, then, 
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