Can you eat fish? Fish is a good source of protein and low in calories too. Nuts are good as well.

> I got some protein powder and tried to mix it up and it's one of the worst tasting things I've ever tried.

Is it flavoured? Maybe you can find a nicer flavour? Chocolate flavour seems to cover a multitude of nastiness (IMHO) but strawberry might be good if you aren't into chocolate.

> I can have very little fruit and all of it has to be canned.

Hmm... Canned fruit tends to have preservatives and additives and often added sugar / syrup. Is there anyway you could switch to fresh or frozen? Maybe by cutting up fruit and freezing it?

> I put in 1 cup lactose free low fat milk, 4 ice cups, the powder and 2 scoops of frozen yogurt. I managed to keep it down but it doesn't taste very good. Do you have any ideas?

Yep.

Needs more flavour.

Some things that help with flavor include:

Fruit. An apricot goes a long way. Peaches, nectarenines, mangos etc are all good for smoothies. Berry fruits are great, too. If you blend the berries for a while you might be able to strain the fruit if you don't like the pips. Or... If you let the shake settle for a bit all the pips will sink to the bottom and so you could pour the pip free shake off the pips for a pip free shake that tastes better.

Flavouring essences. Vanilla essence etc. Maple syrup is great as a sweetener and flavour enhancer.

Things tend to taste better when they are very cold (because the cold helps numb your tastebuds too. Does your smoothie maker crush ice? If it does then you could make flavoured ice cubes. For example, you could put yoghurt (better for you than frozen yoghurt, typically) into ice cube containers and use the yoghurt ice cubes to cool and flavour your smoothie. Or you could put the milk into the ice cubes. If you suck on an icecube of any variety before drinking the smoothie then the smoothie should taste better because you will have numbed your tastebuds some.

If you were into chocolate then cocoa would help flavour the smoothies too. Because it is strongly flavoured. An alternative would be coffee (decaf even).