According to the New Scientist article others have linked to, the equivalent human dose was 9-12 packets of sweetener a day. I'm sure there are heavy coffee drinkers that go through that much.
I also don't like those studies where the human equivalent dose is like 50 pounds of sweetener a day, or something silly. This one isn't so bad.
I guess I'm having trouble figuring out where the numbers are coming from.
I'm seeing that the FDA recommended maximum dose for aspartame is 50mg/kg/day. Assuming a 70kg Standard Man, that's 3.5g/day of aspartame. Diet Coke has 125mg per 12oz. can, so that would be 28 cans/day. Each packet should be around 35mg aspartame, so 100 packets/day (the amount of aspartame per packet was hard to find, and the approx. was from an American Cancer Society article).
Agreed that 9–12 packets doesn't sound like much, but I think we're talking way more than that.
For comparison, that amount of sweetener (9-12 packets) is found in about 3 cans of Diet Coke (35mg aspartame per packet, 125mg per Diet Coke). I suspect there are quite a few people who consume more than that in a day.
One criticism however would be that the dose of artificial sweetener tested was atypically high.
It'll be neat to see further research into the cause of variable responses of the subjects to the artificial sweeteners.