Inflation hawks, beware.

A sudden spike beyond the Federal Reserve's 2% target could slam bond and equity markets, Charles Ellis, author of the legendary investing book "Winning the Loser's Game," said this week on CNBC's "ETF Edge."

"The cost of money is so low that after you adjust for inflation, bonds don't pay anything," said Ellis, the founder and former managing partner of Greenwich Associates.

"If bonds are a bad bet because of inflation, the inflation is going to affect equities as well and it will reduce the value of equity securities, no doubt about it," he said.

Bonds are Ellis's latest fascination, a new chapter in the eighth edition of "Winning the Loser's Game," released on Tuesday.

According to him, the traditional 60-40 stock-bond tilt has become outdated, with investor individualism taking precedent.

Each investor has a "different amount of wealth, different amount of income, different amount of savings capacity, different attitude towards risk," Ellis said.

"When you take all of those different things and a different time horizon, ... that's what should be governing your way of investing," he said.

Having 30-40% of your portfolio in bonds as someone who is able to save a substantial amount of money may be misguided, for example, Ellis said.

"There may be somebody in the world for whom that is the correct answer, but they're not very many and they certainly aren't everybody," he said.

With interest rates so low, ETF investors in particular should be careful dabbling in bonds, ETF Trends chief investment officer and director of research Dave Nadig said in the same "ETF Edge" interview.

"Bonds in a portfolio have always behaved differently than an individual bond," he said. "In a portfolio of constantly rebalancing bonds, that's a very different pattern of returns."

To Nadig, part of the problem is that bond investors aren't being paid well enough for the risk they're taking.

"There are multiple things going on there that just make bonds a very difficult asset class to own right now," he said. "It doesn't mean that an individual bond can't still serve a specific purpose for somebody. I know plenty of advisors who are still building individual bond ladders for certain clients with certain needs. But the blanket idea that as an asset class you can just put money in the AGG and it will do a certain thing for you, I just don't believe it's true right now."

AGG is the iShares Core U.S. Aggregate Bond ETF, down just over 4% from its all-time high made last August.

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