Food is a basic necessity to sustain life. With such a fundamental demand serving as a constant tailwind, you might think food stocks should have no trouble producing satisfactory growth. But the truth is that not all food stocks are created equal. Within the food industry, there are subtle yet definite changes occurring in consumer buying habits and eating preferences. Now that we're in an age of health-consciousness, Americans are shying away from products that are perceived as unhealthy, namely canned and frozen packaged foods. This is serving as an anchor on growth for many food companies, including ConAgra Foods (CAG -0.46%) and Campbell Soup Company (CPB -0.94%). But while ConAgra and Campbell are showing the effects of changing consumer tastes, PepsiCo (PEP -0.34%) -- which sells a range of drinks and snacks it deems "fun for you," like Mountain Dew and Doritos; "better for you," like Baked Lays chips and SoBe lifewater; and "good for you," like Quaker Oats and Sabra hummus --seems to have it figured out.

Canned and frozen foods are out
For the past year, ConAgra's and Campbell's earnings reports have contained little in terms of good news for investors to celebrate. ConAgra's diluted earnings from continuing operations declined 16% last quarter year over year. Weakness was most pronounced in its consumer foods group, which includes the Healthy Choice, Chef Boyardee, and Orville Redenbacher's lines. ConAgra's consumer foods segment posted a 1% sales decline last quarter year over year, as its key Healthy Choice brand remained a poor performer. In response, management has aggressively increased marketing of its higher-performing Cafe Steamers line.

Campbell recently reported fiscal-first-quarter results of $2.25 billion in sales and $0.74 per share in adjusted earnings. Sales and adjusted EPS grew 4% and 12%, respectively, year over year. This looks good on the surface, but there are a couple of important points to note. First, Campbell benefited from the timing of its first-quarter results. The first quarter of its fiscal year ended one week later than the first quarter last year, leading to a higher capture of Thanksgiving-related sales, which is basically just taking away from second-quarter sales. Second, Campbell management reduced its forecast for the full fiscal year in its earnings report. The company expects flat to 2% sales growth this year, and a 1% decline to a 2% increase in adjusted earnings per share for fiscal year 2015.

The push toward fresher foods with better-sourced ingredients is clear, yet neither ConAgra nor Campbell has been able to capitalize on these trends thus far. To be sure, both companies have tried to shake up their brands with new product releases, but their attempts haven't gained much traction. Campbell sells organic products through its Bolthouse Farms line and also sells organic Swanson broths, Wolfgang Puck soups and Plum Organics baby food. It also is set to launch Campbell's Organic soups in January. However, Campbell's organic brands make up too small of a piece of the total company to have much of an impact.

Snacks and oatmeal are in
ConAgra and Campbell are struggling, but by comparison, PepsiCo's food business is doing very well. This is particularly true when it comes to snacks. PepsiCo owns the Frito-Lay and Quaker brands, which sell chips and other snacks that aren't considered healthy, but are selling nonetheless. This is particularly true in the emerging markets, where PepsiCo is hitting the ball out of the park. PepsiCo expects to generate 9% earnings growth in the current fiscal year, driven largely by its snacks business. Organic revenue grew 9% for Frito-Lay in Latin America last quarter year over year. PepsiCo generated 11% revenue growth in Asia, the Middle East, and Africa, driven by 11% volume growth of snacks. Pepsi's earnings per share rose 11% last quarter year over year, excluding the effects of currency fluctuations.

ConAgra and Campbell can't seem to get a handle on what consumers want, while PepsiCo's sales and earnings numbers are much better. That's why I think investors should avoid ConAgra and Campbell Soup, and stick with PepsiCo.

Editor's note: This story has been edited to reflect the breadth of Campbell's organic offerings.