Eating DE will not do anything for bugs. I doubt that it would even do anything for worms in your gut. It may have other beneficial effects when ingested, but it will not do anything for bugs.
DE works on bugs chiefly by cutting their chitinous exoskeletons. Being cut, or abraded, the insect then dehydrates and eventually dies. Insects that groom are the most susceptible to DE.
Bedbugs do not groom. They do not dehydrate easily. They get all their hydration from the blood they ingest. A fully fed adult can live for over a year without feeding again.
The best thing to do for bedbugs seems to be a regular routine of activities that control and eventually eradicate the pests. Given the insects durability, these routines may need to be kept up for a long time. With heat being the best weapon, the best timing for bedbugs eradication would seem to culminate in the summer months.
Wash bedding frequently. Wash in hot water. Dry bedding at the highest heat setting on a clothes dryer. If you hang out your laundry, or even if you use a dryer, bag the bedding in a black trash bag. Leave the bag in the sun or stash it in the car. High heat kills the pest. Freezing will work also, but you must get to 20° F or less.
Use beg bug traps. This is actually my own idea based on observations. Bedbugs like to hide in small spaces. I notice they love to hide in the books I sleep with (I fall asleep reading each night). Make "books" from white paper and leave then about the room, in the bed, etc. Collect them every so often and bake them in the oven before reuse. Incidentally, bedbugs will survive 2 minutes in a microwave oven.
Lastly, keep a roll of scotch tape on the night table. Use a plain white sheet on the bed. The adults are easy to spot. The nymphs are tiny, perhaps 1/10th of a pin head. When you see a bedbug moving on the sheet, stick it up with a spot of tape. Fold it over to seal the pest inside. Bedbugs seems to emerge about an hour or so after you get in bed. Set an alarm to wake you for bedbug patrol. Dispose of them by baking or burning.
If you must get rid of furniture (the solar baking method could save an expensive mattress) then spray paint "bedbugs" on it so someone else won't be tempted to take it and feed the critters elsewhere.
OK, so I've now given a lot of info on bedbugs. I would love to hear from others who have had success getting rid of this pest.