For who says that  “A calorie is a calorie” in this perspective mean to suggest that macronutrient proportions are extraneous to weight management. All that substances are the total number of calories consumed, in spite  of whether the plurality comes from fat or carbohydrate.
It sounds reasonable, but it’s actually it’s wrong. A calorie is not a calorie, in more than one sense. Carbohydrate, fat and protein calories are indeed equal by label in terms of their energy content, but the body processes each in a distinct way, and these differences have real propositions for weight management. In connection, food calories of all categories may have very different effects on the body depending on when they are eaten and what they are eaten with. Below are the  five particular reasons why all calories are not equal.
1. The energy cost to metabolize fat, carbohydrates and protein are not the same
The body must consume energy to digest, take in and metabolize the energy in food. It so happens that the body consumes dissimilar quantities of energy to process different energy-containing nutrients. In general,  additional energy is required to process protein than carbohydrates, and additional energy is required to process carbohydrates than fat.
2. Calorie constraint slows metabolism
The major problem with using linear calorie equations for fat loss is that the lesser calories you intake, the lesser calories your body burns. Therefore, if, based on the 3,500-calorie rule mentioned above, you make a decision to cut your daily energy consumed by 500 calories in hopes of losing a pound a week (500 calories/day x 7 days = 3,500 calories), you will most likely find that you do certainly lose a pound in the first week but fewer  in each following week. This incident is believed to represent a metabolic adaptation to prevent malnourishment. Your body exactly runs cooler to conserve the reduced number of calories you’re eating, thus effectively increasing the value of each calorie.
3. Protein decreases appetite
Protein in general decreases appetite more per calorie than fat and carbohydrate. Thus ,a person who increases his daily protein consumed without making any conscious attempt to eat less is likely to eat less in any case due to reduced appetite. This is one more important sense in which protein, carbohydrate and fat calories are not equal.
4. Fiber decreases calorie amalgamation
Fiber is a form of carbohydrate that contributes to satiety without contributing calories, because it is not being absorbed into the body. as a result, a 100-calorie high-fiber food will decreases appetite and succeeding eating more than a 100-calorie low-fiber food. Similarly, a person who increases his daily fiber consumption without making any conscious effort to eat less will wind up eating less anyway due to reduced appetite. Thus, a calorie inside a high-fiber food is not equal to a calorie inside a low-calorie food-yet a fourth way in which “a calorie is not a calorie.”

There were lots of foods contain substances other than vitamins and minerals which are very important  for health. Known as phytochemicals, these substances are antioxidants that help to protect against coronary heart disease and cancer. Take note of the low-calorie food you should eat on a regular basis.

1. Citrus Fruits Lemons: 19kcal/100g Oranges 37kcal/100g

Citrus fruits such as oranges, lemons, limes and grapefruit are an excellent source of antioxidant bioflavonoids and vitamin C - a single fruit usually provides the recommended daily amount of 60mg per day. Oranges contain the flavonoid, hesperidin, while grapefruits contain the flavonoid naringenin. These work together with vitamin C to boost its antioxidant effectiveness, and may also have anti-cancer properties. Citrus fruits contain pectin - a soluble fibre that helps to lower a high cholesterol level. Lemons are a rich source of lemonoids and limonene - phytochemicals that protect against cancer.

2. Broccoli 33kcals/100g

Broccoli is now recognised as one of the most beneficial green vegetables, as it contains a number of phytochemicals that help to protect against cancer. It only contains 2% carbohydrate but will boost your protein, calcium and magnesium levels. It is a good source of weak plant oestrogens such as genistein, that are converted into biologically active hormone-like substances by intestinal bacteria, especially when the diet is also rich in fibre. It also contains indole-3-carbinol, a substance needed to metabolise sex hormones in the body more efficiently.

3. Carrots 35kcal/100g

Although they are only 8% carbohydrate, carrots are an exceptionally rich source of carotenoids – the yellow-orange pigments that give carrots their vibrant colour. Carotenoids have an important antioxidant action in the body. Some carotenoids such as alphacarotene and betacarotene can also be converted to vitamin A in the body and are therefore known as pro-vitamins.

4. Grapes 60kcal/100g

Black grapes have long been associated with good health and are traditionally given to hospital patients to help speed their recovery. Red and black grapes contain powerful, antioxidant pigments (eg anthocyanidins, resveratrol) that are believed to contribute to the beneficial cardiovascular properties of red wine plus ellagic acid, which has anti-cancer properties. They provide useful amounts of potassium and trace minerals such as boron, magnesium and copper.

5. Chillis 20kcal/100g

Eating chillies stimulates production of natural painkillers (endorphins) in the brain and mucus in the stomach, which may protect against peptic ulcers. Chillies contain antioxidants, including capsaicin, that also protect against coronary heart disease, cancer and premature ageing. Phytochemicals in chilli peppers thin the blood to reduce the risk of blood clots, high blood pressure and raised cholesterol levels. Good source of betacarotene and vitamin C.

6. Mango 57kcal/100g

Mangoes are an excellent source of carotenoids, some of which the body can convert to vitamin A. Some varieties of mango contain as much as 3g carotenoid pigments per 100g flesh. Mangoes also contain good amounts of vitamin C and fibre, plus useful amounts of potassium and vitamin E.