Types of Diets



Diets are made up of three distinct food types; carbohydrates, fats and proteins. The dietary guidelines present food groups or pyramids to ensure the general public consumes 55% carbohydrate, 30% fat and 15% protein.

Even though the concept of weight or fat loss is a simple negative caloric balance, many dietary interventions incorporate diet plans that are not balanced per the US guidelines. These include

  • High-Protein
  • Low Carbohydrate
  • Low Fat

The problem with most of these diets is when one component is changed, the other two must adjust accordingly.


High protein diets are based on the protein content of the diet being 30% or larger. The average high protein diet is illustrated to the right. However, the range of protein content in the literature is 30-100%.


Obviously, as illustrated to the right, when the protein is increased, the carbohydrate content becomes lower.

Very low carbohydrate diets decrease the carbohydrate content as low as 8%.

Both the protein and the fat increase in low carbohydrate diets. Fat content has a larger increase.

Low-carbohydrate diet of higher carbohydrate content; yet under the dietary guidelines for carbohydrate


High protein diets are the most popular type of diet recommended for weight loss. Protein diets can be administered in the form of a liquid diet, foods of limited variety, or a more varied menu. Even though there is no formal definition for high protein diets, Eisenstien and colleagues reports the characteristics of the high-protien diets found in the literature to be > 25% for adults who are in stable weight and >35% for weight loss conditions.

The advantages for high-protein diets are:

  • Satiety - increased with proteins
  • Palatability
  • Suppress Hunger
  • Thermogenesis - the thermic effect of food is = 0.132 (/ gram protein); 0.051 (/ gram fat); and 0.054 (/ gram carbohydrates).

The risks of high-protein diets include:

  • Calcium homeostasis - excess protein increases Ca++ excretion leading to bone reabsorption and osteoporosis
  • Low-grade metabolic acidosis - from calciuresis
  • Nephrolithaisis - or kidney stones, both uric acid and calcium stones
  • Increased cancer risk - from the oxidative stress of beef and pork. Soy protein has been associated with increased breast cancer risk

On the other hand, a high-protein diet is prescribed for kidney disease as it delays the progression of kidney disease.

Plotting the weight loss results of eight studies (with control groups) Eisenstein found a relationship between percent protein and weight loss. However, the higher protein diets were also ketogenic. These diets ranged from 300- to 1385 kcal/day; with the mean being 743 kcal/day. The duration of the diets ranged from 3 -10 weeks; mean 5.325 weeks.

How much of these weight losses come from the quality of the high-protein vs. the negative caloric balance?

Types of Diets


Recently low-carbohydrate diets have increased in popularity because of their rapid weight loss. The Atkins diet fits into the low-carbohydrate class of diets. Low-carbohydrate diets are high in protein and fats. This increase in protein with low-carbohdrates have been proposed to promote the metabolism of adipose tissue in the absence of available dietary carbohydrate. Some diets control the carbohydrate intake with no limitations on fat or protein, whereas others recommend complementing the low-carbohydrate diet with vegetables and fruits high in fiber or unlimited protein with caution on fats. The average adherence rates to low-carbohydrate diets is 61.4%; the duration of the trials was not stated.

Similar to the high-protein diets, the risks include

  • ketone accumulation
  • impaired kidney and liver function
  • in salt and water depletion
    • postural hypotension
    • fatigue
    • constipation
  • Hyperlipidemia


Bravata and colleagues reviewed 107 studies of 94 different low carbohydrate diets between January 1, 1966 and February 15, 2003. They divided the diets into very low carbohydrates (left panel below) and low-carbohydrate (right panel below) diets; based on a 60 g/day intake.

The very low-carbohydrate diets exhibited more weight loss than the low-carbohydrate diets.

The largest weight change for the very low-carbohydrate diet was in the first two weeks.

BMI changes were similar.

Percent body fat changes were similar.



No changes or differences were found in Cholesterol or blood pressure; however all values were normal to begin.

They concluded that there was insufficient data to to make recommendations for or against low-carbohydrate diets. There needs to be more studies on the use of the diet beyond 90 days, for adults >50 years old as well as the use of these diets with patients with hyperlipidemia, hypertension and diabetes.
Types of Diets


Low-fat diets are typically high in carbohydrates. Astrup and colleagues summarized 19 studies on low-fat diets between January 1966 and July 1999. In these diets, dietary fat was reduced an average of 11.12% fat (range 3 to 18.7%); each had a control group that did not change fat intake. Individual study weight loss is illustrated below; the average weight loss for the 19 studies was -2.82 kg for the diet groups and 0.384 for the control groups

The duration of these diets ranged from 9 weeks to 12 months. Risk for low-fat diets was not assessed in this review; neither was the effects of the diet on risk factors.

Types of Diets




The graph to the right illustrates the weight loss of the studies selected by Nordmann and colleagues for the meta-analysis on low-carbohdrate diets. Long-term weight loss was the focus of this meta-analysis.


Of secondary importance in the low-carbohdrate diet was its affect on risk factors and the comparison to low-fat diets.

Low-carbohdrate diets exhibit larger weight loss than low-fat diets.

The changes in systolic blood pressure do not appear to be different between low-carbohdrate and low-fat diets. However, these results should be interpreted with caution. The presenting blood pressures were not high. Some were prehypertensive. Changes in blood pressure are not expected with normal blood pressures.

Similar results were found with diastolic blood pressures.

The changes in total cholesterol appear to be larger in low-fat diets than in low-carbohydrate diets. Low-fat diets are effective even in conditions of normal cholesterol.
Changes in Triglycerides are the most dramatic between Low-carbohydrate and low-fat diets. Low-carbohydrate diets produce larger decreases in triglycerides than high-fat diets.

Samaha and colleagues compared low-carbohydrate and low-fat diet effectiveness in severe obesity. These subjects were matched for severe obesity, diabetes and metabolic syndrome. The study began with 132 adults divided into the two diet groups; but ended with 79. Dropout was more rapid in the low-fat diet group (47% at 6 months) than in the low-carbohydrate diet group (33% at 6 months). The low-carbohydrate group was instructed to consume less than 30 grams/day; whereas the low-fat group as instructed to lower their caloric intake 500 kcal and limit fats to 30% or less.

The table below summarizes the characteristics of the food intake at 6 months into the intervention. Caloric intake was not significantly different between the two groups. Protein and carbohydrate content were lower in the low-fat diet; whereas carbohydrate content was highest in the low-fat group.

The figure on the right illustrates the weight loss of the two groups. The low-carbohydrate diet lost more weight than the low-fat diet.
Similar to the review above, triglycerides exhibited the largest decrease with the low-carbohdrate diet. No other changes in HDL LDL or total cholesterol were found; although may subjects were taking antilipidemic medications. Glucose decreased significantly in the low-carbohydrate diet in both diabetic and non-diabetic subjects. No data were reported for blood pressure.
Types of Diets


The Mediterranean Diet is not necessarily a weight loss diet. It is more associated with longevity and quality of life. The Mediterranean Diet is characteristic of countries of southern Europe; France, Spain, Greece and Italy in the early 1960s. It is primarily comprised of

  • Plant foods (fruits, vegetables, breads
  • Minimally processed, seasonally fresh and locally grown
  • Fresh fruits as dessert with sweets based on nuts, olive oil, and concentrated sugars or honey during feasts
  • Olive oil as the principal source of dietary lipids
  • Diary products (mainly cheese and yogurt) consumed in low to moderate amounts
  • Fewer than four eggs per week
  • Red meat consumed in low frequencies and amounts
  • Wine consumed in low to moderate amounts, generally with meals


128 studies focusing on the Mediterranean Diet were reviewed. The Mediterranean diet has been documented to


  • BMI
  • Total Cholesterol
  • Triglycerides
  • Glucose
  • Insulin
  • C-reactive protein
  • IL-6
  • IL-7
  • IL-18
  • insulin resitance
  • vascular cell adhesion
  • oxidative biomarkers
  • HbA1c
  • free fatty acids


  • endothelial function
  • HDL
Types of Diets


Dansinger and colleages observed the weight loss and cardiovascular risk factor changes with four popular diets.

  • Atkins - is low-carbohydrate with without fat restriction
  • Weight Watchers - restriction of portion sizes and calories
  • Zone - modulation of macronutrient balance and glycemic load
  • Ornish - low-fat

160 overweight adults (mean 36; range 27-42 kg/m2 were randomly assigned to the four diets for 12 months.

The caloric intakes of all the diets were similar; Atkins diet may have had a higher caloric intake.
The nutrient content of the four diets were similar for protein; whereas the fats were highest in Atkins and lowest in Ornish; and carbohydrates were opposite.

Adherence to all four diets was similar

The weight loss was modest. The weight loss for each diet was significantly different.

There are differences in cholesterol reduction with these diets.

Atkins reduces cholesterol the least whereas Ornish decreases cholesterol the most.

Similar findings are with LDL cholesterol whereas HDL cholesterol is similar for all four.

Changes in systolic blood pressure are not as good for the Ornish diet as the other three.

Diastolic blood pressure responds similarly.

Glucose, on the other hand, lowers more with the Atkins and Zone diets.
It turns out that the changes in most of the risk factor depend on the weight loss.
Types of Diets



In a meta-analysis of 493 studies from 1969-1994, Miller and colleagues found greater weight loss with diet and diet + exercise, but less loss of lean weight with exercise in middle-aged moderately overweight adults.

The mean weight loss for diet in Miller's review is different from the mean weight loss in the diets presented above.

It is important to note the energy expenditure of these studies was not constant throughout these papers.

Skender and colleagues provided diet, exercise and diet & exercise interventions for 127 adults for 12 weeks followed by three biweekly and then three monthly maintenance sessions. Behavioral techniques for all three groups were

  • Contracts
  • Stress management
  • Stimulus control
  • Goal setting

The measured variables at 0, 3, 12 and 24 months; with a drop-out of 64% in the diet group, 41% in the exercise group and 50% in the diet/exercise group.

They concluded that diet produced quick weight losses which were reversed. Exercise was the factor for weight loss maintence.
Types of Diets

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