If it is already close to reaching full market penetration then eventually your competition will become too fierce.
There will be too many fish in a small pond.
Also, if you are marketing online, can your product be shipped worldwide?
Many nutritional products suffer from a maze of complicated legalities in different regions which may prevent you building a global business.
Information products are not normally subject to the same restrictions and are thus much more suitable for global online marketing.
So look at the products you are planning to market, ask yourself if they can be marketed anywhere in the world and find out if the company has plans to expand globally in the future.
Click here to learn about a company which still has huge growth potential and is active in well over 100 countries.