Different types of calories used by the body

A calorie is a calorie. All calories are units of fuel for your body. But the type of calorie does determine how it is processed. This depends on whether your body needs fuel after eating or if some will be put into storage.

Bottom line: All calories can be converted to fat if too many total calories are eaten, but fat calories have no alternate pathway options. Either use fat as a fuel then or store it as fat for later. Both carbohydrate and protein have alternate fuel pathways so they are one step away from fat storage.
Here are the possibilities:

Carbohydrate calories

1. Used quickly as sugar fuel, if you need it.
2. Stored as carbohydrate (glycogen), especially likely if you exercised earlier that day
3. Converted to fat for storage if glycogen stores are plentiful.

Fat calories

1. Used quickly as fat fuel, if you need it
2. Stored as fat. (There is no conversion of fat to another fuel type. But they won’t be stored unless you have eaten more TOTAL calories than you need)

Protein calories

1. Used as raw material to build body parts (not fuel)
2. Converted into sugar for immediate use if needed
3. Converted into fat for storage if not needed
Shifts during weight loss

There are 3 energy shifts that occur after you begin weight loss or create a calorie shortage for your body. Fat is used in the early stages, but not as readily as it will be when your body sustains the low calorie diet.

The bottom line: If you consistently keep your calories low for more than just a couple of days, fat stores will become the primary supplier your back-up fuel.
3 energy stages

Stage 1 Calorie intake is below calorie expenditure Carbohydrate and Fat storage are utilized as back-up fuel to support energy needs. Water is released as carbohydrate stores are used up. This accounts for 70% of weight loss in first 3 days of a calorie deficit.

Stage 2 Carbohydrate stores are lower Blood sugar level may be lower. Hunger sensitivity increases. May feel grumpy, lightheaded or weak at times during the day. Strenuous exercises are likely to bring on low blood sugar symptoms since they use more sugar. Eating small carbohydrate with protein snacks between meals will help raise blood sugar if it has a tendency to dip.

Stage 3 Fat becomes the primary back up fuel for energy needs Fat mobilization for fuel source increases. Blood sugar may stabilize and symptoms of stage 2 become less common. Fat is mobilized readily with long aerobic exercise sessions that are not too strenuous.

High protein, low carbohydrate diets

When carbohydrate in the diet is kept too low, the body changes its fueling system after about 3 days. As existing carbohydrate stores are used up, the body turns to fat and protein for fuel.

The bottom line: This diet can have a negative effect on blood pressure, diabetes and heart disease. Losing minerals, especially calcium, isn’t good for your bones. Low carbohydrate, high protein diets do “seem” to work because weight loss is dramatic and quick. But much of the weight lost is due to dehydration and carbohydrate store depletion. One pound of water = 2 cups. Not much water to celebrate a pound of weight lost. Don’t be fooled. These diets can create, or worsen, many health problems.


Role during carbohydrate restriction

Waste Produce

Body Adaption

Fat Becomes the main fuel of muscles at rest and with light exercise. Keystone Suppresses appetite. Blood acidity rises. Kidney workload increase. High water losses. Risk of dehydration on this diet. Increased loss of calcium, sodium and potassium. Exercise tolerance goes down.


Broken down into carbohydrate needed to fuel the nerves, the brain. Muscles also need carbohydrate during strenuous exercise

Urea Increased work for kidneys. Increased water, calcium and other minerals lost in urine. Exercise tolerance goes down
Very Low Calorie Diets

Any diet that is 800 calories or lower is defined as a very low calorie diet. These diets are usually provided as liquid or food bar nutritional supplements because the nutrient composition required for very low calorie diets to be safe is hard to match with regular foods. The rate of weight loss for most people on a VLCD is rapid (greater than 3 pounds per week), and risks are involved with this.

Bottom Line: These diets should be only be undertaken with medical supervision and monitoring, and are restricted to individuals who meet the criteria for severe obesity (BMI above 35) and have been unable to lose weight with more moderate approaches.
Weight Loss Drugs

Weight loss drugs prescribed by physicians are effective but produce only moderate weight loss results (Range = 4.4 to 22 pounds). Drug therapies for weight loss have potential side effects, and are only recommended for individuals who have health problems related to obesity, or for those who are significant obese and are unable to lose weight with diet and exercise changes alone. Even then, drugs may be suggested as an adjunct to, not replacement for, the diet, exercise and lifestyle modification.

Over-the-counter drugs which claim to suppress appretite are not effective for weight loss. As tolerance is reached, their effect wears-off. Higher doses are quickly required, making these products very dangerous. Extreme blood pressure elevations and heart problems are possible.

Bottom Line: Weight loss drugs do not replace diet, exercise and lifestyle modification in importance for weight loss and weight maintenance.

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