"Sure, these restaurants try to look good by introducing a few healthier items, but when one considers what and how they market and what they offer incentives to buy (with package meals), the picture is not a positive one," said Brownell.
Right or wrong, diet and public health experts agree Taco Bell's new campaign will likely seriously influence Americans who spend a great deal on fast food from their cars each year.
"The entire restaurant industry is $390 billion a year, fast food is $230 billion of that," said Tom Wagner, vice president of Consumer Insights for Taco Bell.
Although the line of "Fresco" burritos and tacos has existed for six years, the upcoming weeks will be the first time the majority of Taco Bell customers will see the low fat options on the menu.
"They've been on the menu for several years, but people had to look for it inside," said Ruth Carey, a dietician and spokeswoman for the Taco Bell Drive-Thru Diet menu.
Along with Christine, Taco Bell will move the Fresco option -- swapping cheese and high-fat sauce for salsa -- out to the drive-thru and package it in the Drive-Thru Diet menu.
"Seventy percent of business is on the drive-thru," explained Wagner.
Dieticians reached by ABCNews.com thought the items on the Taco Bell Drive-Thru Diet menu had a good handle on calories and fat, but had pitfalls in terms of salt and nutritional value.
Bonnie Taub-Dix, spokeswoman for the American Dietetic Association, pointed out that the Fresco Crunchy Taco, for example, "barely has protein" and that "half of the calories in that meal are coming from fat. If someone had this for lunch alone, I'd say it's an inadequate lunch."
She was happy with the protein in the Fresco Burrito Supreme With Chicken, but not the salt.
"The fat of that one is 70 out of the 340 calories," said Taub-Dix. "If you look at the sodium content, it's 1,410 milligrams, which is really about what you need for the whole day."
Carey, who is also a sports nutritionist with the NBA alongside her work with Taco Bell, agreed that the salt content was high.
"Taco Bell is aware that these Fresco items [contain] higher sodium than other items, and they're trying to find ways to lower the sodium and maintaining the taste," said Carey. But, she added, "any of those items can fit in moderation -- be aware that the rest of your day needs to have meals in lower sodium."
Yet, some dieticians don't think those types of caveats will translate to the drive-thru on a busy day, or in the noise of other fast food commercials and marketing.
"Yes, [Christine] said it took her two years and yes, she said her results were not typical, but I bet many people can't recall hearing that the first time they see or hear this spot," said Dr. Stephen Cook, of Golisano Children's Hospital at the University of Rochester Medical Center in New York.
"There really shouldn't be a forbidden food, but it's tough for human nature to think in a moderate fashion when our perception of what is a normal serving size of a meal is lost in today's market place."