Which is healthier for diabetics--boiled sweet potatoes or steamed sweet potatoes? Sliced or whole?

My aunt who is in her sixties was recently diagnosed with diabetes. She loves to eat sweet potatoes but I'm not sure which is a healthier choice for her--boiled or steamed sweet potatoes? And is it healthier to slice them before cooking or cook them without cutting?
Thanks!
Which is healthier for diabetics--boiled sweet potatoes or steamed sweet potatoes? Sliced or whole?
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