Eating a very low caloric yet nutritionally balanced diet is good for your heart and may improve longevity. Animal studies have confirmed that feeding fewer calories increases life span, but human studies have not been done.  There are 3500 calories in a pound. If you're burning 75 calories a day, it would take about 46 days to lose one pound.

Daily caloric intake
Minimum daily caloric need is 1200 calories per day for women, and 1800 calories per day for men. However this varies widely depending on physical activity level.

Caloric restriction diet and food restriction
Caloric restriction diet tends to resemble a traditional Mediterranean diet, which includes a wide variety of vegetables, olive oil, beans, whole grains, fish and fruit. The diet avoids refined and processed foods, soft drinks, desserts, white bread and other sources of so-called "empty" calories. Research on mice and rats has shown that stringent and consistent caloric restriction increases the animals' maximum lifespan by about 30% and protects them against atherosclerosis and cancer, but human study has been difficult because the caloric restriction lifestyle requires a strict diet regimen, both to keep the total number of calories low and to insure that people consume the proper balance of nutrients.

Caloric restriction and longevity
Evidence already exists to suggest that calorie restriction increases maximum life span in several animal species. However, there hasn't been any definitive proof of caloric restriction having similar effects in humans. being the case in humans. But recently researchers enrolled 48 healthy overweight (but not obese) men and women in a 6-month trial looking at the effects of calorie reduction. Participants were assigned to one of four groups: a control group, which followed a normal diet; a caloric restriction group, which received 25 percent less calories than the daily requirement; a third group, which exercised and reduced calorie intakes (12.5 percent calorie restriction and 12.5 percent increase in energy expenditure); or a group that received a very low calorie diet, starting with 890 kcal a day and then increased to maintain a 15 percent weight loss. After 6 months, while patients in the control group lost about 1 percent of their weight, both calorie restriction groups (with or without exercise) lost approximately 10 percent. Individuals on the very low-calorie diet lost nearly 14 percent of their weight. There was lower blood levels of insulin after fasting and a lower body temperature in all participants who undertook a restricted calorie regimen. Apparently, body temperature and blood insulin levels are markers of longevity like gray hair or wrinkles can be. There have been reports that both in animals and humans that those with lower body temperature tend to live longer. Less DNA damage seemed to occur in patients with lower caloric intakes. JAMA 2006.

Caloric Restriction and Thyroid Hormone
While exercise helps ward off chronic ailments such as obesity, diabetes, and heart disease that can shorten a normal lifespan, only caloric restriction appears to slow down the primary aging process. Eating a low-calorie, nutritionally balanced diet lowers concentrations of a thyroid hormone known as T3, which controls body temperature, cell metabolism, and it appears the production of free radicals - all of which are important aspects of aging and longevity. Calorie restriction also decreases levels of the inflammatory protein tumor necrosis factor (TNF)-alpha.

Caloric Restriction and Heart Health
Studying heart function in members of an organization called the Caloric Restriction Society, investigators at Washington University School of Medicine in St. Louis found that their hearts functioned like the hearts of much younger people. Ultrasound examinations showed that the hearts of people on caloric restriction appeared more elastic than those of age- and gender-matched control subjects. Their hearts were able to relax between beats in a way similar to the hearts in younger people. In Western countries, heart attacks and strokes are responsible for about 40% of all deaths. Cancer causes about another 30%. Deaths in both groups can be attributed to what scientists call secondary aging. That's the term used to characterize health problems that result from conditions such as high cholesterol, diabetes, high blood pressure and other preventable conditions that contribute to premature death. A healthy diet and regular exercise can reduce risks from secondary aging. But this study suggests calorie restriction with optimal nutrition can do even more. People on the very low-calorie diet have low blood levels of cholesterol and triglycerides, blood pressure scores equivalent to those of much younger individuals, a lower risk of developing diabetes and reduced body fat. These markers indicate less secondary aging. Meyer TE, Kovacs SJ, Ehsani AA, Klein S, Holloszy JO, Dr. Fontana L. Long-term caloric restriction ameliorates the decline in diastolic function in humans. Journal of the American College of Cardiology, 2006.

Caloric restriction and bone strength
Men and women who lose weight through caloric restriction, without exercise, also lose bone at the hip and spine, increasing their risk for the bone-thinning disease osteoporosis and fractures. Adding regular exercise to a calorie-restricted diet helps shield the bones from the harmful effects of caloric restriction dieting.

Caloric restriction and immune system
Caloric restriction seems to boost key infection-fighting cells in the immune system. Dr. Janko Nikolich-Zugich, a senior scientist at Oregon Health & Science University's Vaccine and Gene Therapy Institute says calorie restriction has been shown to reduce the aging of the immune system in rats. And calorie restriction has also been shown to increase the life span of yeast, worms, flies, zebrafish, and spiders. This same benefit may also hold true for monkeys.
"Under long-term caloric restriction, that was started in young adult monkeys, there is a very remarkable way of preserving both the form and the function of the immune system, which will result in much better resistance to infectious disease," Nikolich-Zugich said. In the 42-month study, Nikolich-Zugich and his colleagues found that calorie restriction improved the maintenance and production of T cells in 13 rhesus monkeys, 18 to 23 years of age, whose calories were restricted, compared with 28 monkeys who ate a normal diet. The researchers found that calorie restriction improved T cell function and reduced the production of inflammatory compounds. These findings suggest that limiting calories can delay immunological aging, and, in turn, life span maybe increased by providing longer-term resistance to infectious diseases.

Recommended Caloric intake for Weight Loss
Unless you are suffering from significant obesity and are under medical supervision, the lowest recommended calorie intake is 1200 calories per day. There is no need to eat fewer calories. It is preferable to lose weight slowly rather than stress your body with inadequate daily caloric intake to feel good and do your daily activities. Most studies show that increasing exercise combined with moderate caloric consumption (1400-1500 calories) remains the most effective way to lose weight and maintain a healthy weight in the long term.

Caloric requirement
The basic daily caloric requirement is determined by the basal metabolic rate (BMR) - the energy needed to sustain bodily functions (keeping warm, maintaining heart activity, making new cells, and so forth) in a resting state. Caloric requirement is largely genetically determined and generally range between 1,000 and 2,000 calories a day. However, with activity you burn more calories. Exercise increases the BMR.

questions
Is a calorie from one food the same as a calorie from another?
   I am not sure what you mean exactly. Some foods may have a filling effect since the calories are mixed with lots of fiber, so that a person may end up eating less and being still full.