Liz Neporent is a diet and fitness expert and author of 12 fitness bestsellers. She regularly appears on national TV programs and is the president of Wellness 360, a New-York based wellness provider.

For those of us who live in lower Manhattan, Whole Foods is the only game in town. Not that I'm complaining; I'm certainly grateful for the first real supermarket in the neighborhood. After a decade of shopping in cramped, dirty delis where a carton of juice costs double the national average and there aren't any of the good kinds of cereal, Whole Foods is Mecca.

I was pondering these facts as I was grocery shopping the other day. Blueberries were "on sale" for $2.99 a pint. For that same $3, I thought, I could have walked the six steps to the nearest McDonald's (rather than the 10 blocks to Whole Foods) and ordered up a double cheese burger, medium fries and a small Coke. That's three large for two small handfuls of fruit -- or a meal fit for, well, a Burger King.

I can see why people who are even slightly less motivated about their health than I am and are also trying to pinch a penny, would go for the value meal every time. These days, if you have limited cash to feed yourself, it becomes harder and harder to justify itty bitty berries at 10-cents a pop and easier to make a cheapo-but-fattening choice that fills your belly.

Curious to see if there was any science behind this, I did a quick lit search and found a University of Washington study from 2008 that weighed the cost of food against a trait called caloric density. Foods with low calorie density tend to be rich in nutrients like vitamins and minerals (fruits and vegetables, for example) whereas foods with a high calorie density pack lots of calories but tend to be nutrient deficient (these are your Whoppers, your pepperoni slices and your McFlurries.)

Sure enough, the study found that lower-calorie foods do cost more per calorie than the higher-calorie foods. How much more? Based on a standard 2000-calorie diet, the researchers found a diet consisting primarily of calorie-dense foods costs $3.52 a day, but a diet consisting primarily of low-calorie food costs $36.32 a day. (The average American eats a variety of foods throughout the day, spending $7 a day.) To add insult to injury, over a two-year period, healthy food prices jumped a wallet-popping 19.5 percent, while junk food prices actually dipped 1.8 percent.

Factor in the escalating price of a gym membership as well as an escalator next to every staircase, and it's easy to see why so many of us have body shapes that resemble the very blueberries we cannot afford. It's one thing to talk about personal responsibility and making good choices but quite another to realistically translate this into action if you can't even afford basics like bread, milk and eggs, let alone exotic purchases like berries, peppers and tomatoes. To be honest, I don't have all of the answers here. On that day, I put down the berries and picked up the oranges which were also on sale but a better bang for the buck.

What do you usually do? Do you typically give into the lure of a value meal or do you have some tricks for dining on both a calorie and cash budget?