The Commerce Clause does it all; anything goes.

Kagan's Commerce Show-and-Tell
...In exchanges with Senators John Cornyn and Tom Coburn, however, Ms. Kagan showed about as much ankle as we're likely to see on the fact that she would favor a liberal reading of the Constitution's Commerce Clause—a law that was originally written to restrain government power, not expand it.

If Congress passed a law saying Americans were required to eat three fruits and three vegetables a day, Mr. Coburn asked, would that be legitimate under the Commerce Clause? It sounds like a "dumb law," Ms. Kagan wisecracked, which is true enough, but then she added that "courts would be wrong to strike down laws that they think are senseless just because they're senseless." In other words: Congress could do it.

The real question here is whether Ms. Kagan recognizes any limits on the Commerce Clause, which legislators have used as justification to regulate or mandate just about anything, and which the Obama Administration is eyeing as its golden ticket to defend ObamaCare. Some 20 states are challenging the law on the grounds that forcing people to buy health insurance shreds the Constitution.
When it comes to noneconomic activity, Ms. Kagan explained, she believes there are some limits on the Commerce Clause, as the Court laid out in 1995's U.S. v. Lopez on gun laws and 2000's U.S. v. Morrison on violence against women. The Supreme Court's liberals at the time adamantly opposed even that much constraint on federal power, and that means they'll almost certainly find ObamaCare justified as well.
In that spirit, Ms. Kagan maintained that in recent years the Commerce Clause has been read broadly, to suggest "that deference should be provided to Congress with respect to matters that affect interstate commerce" and that "the principal protector against bad laws is the political branches themselves."
That one would have made James Madison howl. When it was written, the Commerce Clause was intended as part of the Constitution's enumerated powers to limit government that could be abused by factions and willful men—that is, by politicians who write "dumb laws."
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