While this is great news for me -- and my wife who has shed 30 pounds -- this is a worrying trend for shareholders of Nutrisystem (NTRI) and Weight Watchers International  (WTW).

The hardest thing for any company is to compete against a rival who gives away a product for free. Microsoft  (MSFT) has faced this problem for years with the Linux operating system, while Apple (AAPL) is fending off a challenge from Google's (GOOG) Android mobile operating system. Both Linux and Android are open-source platforms available for free. Linux's rising popularity is helping push the market share of Microsoft's Windows platform below 90%. Android's market share was 46.3% in the fourth quarter, versus 30% for Apple's iOS, according to Nielsen.

For the weight-loss business, the challenges are similar. The diet industry has to convince heavy people like me that their products and services will enable us to defy the odds and lose weight and keep it off. It's a tough sell given that research has found that "80% of people who have lost weight regain all of it, or more, after two years," according to Women's Health.

Given those daunting odds, why should I put money into a diet program? Many investors and dieters seem to feel the same way.

Nutrisystem, which Monday reported disappointing earnings, is not cheap. The company is running a special offer, which includes its pre-packaged foods, for $195.44 a month. Weight Watchers, which issued disappointing earnings and guidance last year, is less expensive. The company is advertising a three-month savings plan for $56.85 with monthly charges of $18.95 thereafter.   Doctors I consulted seemed to prefer Weight Watchers and the South Beach diet over Nutrisystem.

Losing weight is not rocket science, as I have discovered, though I remain concerned about regaining the pounds that I have lost. I eat right and exercise regularly. My wife makes sure that I keep going to the gym. Lose It keeps me honest by making me aware of the impact of the foods that I consume on my overall well-being. I don't see any reason to change something that clearly is working to my benefit.

Nutrisystem and Weight Watchers face an uphill battle to convince the public that their services are worth the money. As apps become more popular, that challenge will get even more difficult.  These shares should be avoided.

Jonathan Berr is nowhere near his goal weight. He owns no shares listed here.