Ketotic Diets - High Protein and Fat diets.

Summary

1. You will lose weight using these diets

2. These diets tend to be high in saturated fats - these fats can elevate  your blood cholesterol.

2. There is no data on their long term safety.

3. The authors of these diets perpetuate misconceptions about carbohydrates, insulin resistance and misconceptions on the mechanisms of fat loss.

             Dietary Protein and Weight Reduction

A Statement for Healthcare Professionals From the Nutrition Committee of the Council on Nutrition, Physical Activity, and Metabolism of the American Heart Association.

Abstract - High-protein diets have recently been proposed as a "new" strategy for successful weight loss.  However, variations of these diets have been popular since the 1960s.  High-protein diets typically offer wide latitude in protein food choices, are restrictive in other food choices (mainly carbohydrates), and provide structured eating plans.  They also often promote misconceptions about carbohydrates, insulin resistance, ketosis, and fat burning as mechanisms of action for weight loss.  Although these diets may not be harmful for most healthy people for a short period of time, there are no long-term scientific studies to support their overall efficacy and safety.  These diets are generally associated with higher intakes of total fat, saturated fat, and cholesterol because the protein is provided mainly by animal sources.  In high-protein diets, weight loss is initially high due to fluid loss related to reduced carbohydrate intake, overall caloric restriction, and ketosis-induced appetite suppression.  Beneficial effects on blood lipids and insulin resistance are due to the weight loss, not to the change in caloric composition.  Promoters of high-protein diets promise successful results by encouraging high-protein food choices that are usually restricted in other diets, thus providing initial palatability, an attractive alternative to other weight-reduction diets that have not worked for a variety of reasons for most individuals.  High-protein diets are not recommended because they restrict healthful foods that provide essential nutrients and do not provide the variety of foods needed to adequately meet nutritional needs.  Individuals who follow these diets are therefore at risk for compromised vitamin and mineral intake, as well as potential cardiac, renal, bone and liver abnormalities overall. 

(Circulation. 2001;104:1869-1874.)

                    High-Protein Diets and Weight Reduction

 Weight reduction is achieved if there is an energy deficit, that is, if caloric intake is reduced below the level of energy expenditure.  In obese individuals, macronutrient composition of the diet has little effect on the rate or magnitude of weight loss over the short term unless nutrient composition influences caloric intake.  Importantly, however, overall caloric intake depends on the overall palatability of the diet and satiety.  The current average macronutrient composition of the American diet is 12% to 16% of calories from protein, 34% from fat, and 49% from carbohydrate.  The majority of dietary advice has focused on the fat content of the diet because fats provide =9 kcal/g, whereas protein and carbohydrate provide =4 kcal/g.  However, the essentiality and palatability of protein have led periodically to its popularity in numerous diets.

Major shifts in the proportion of one macronutrient result in compensatory changes in the other macronutrients.  Many of the popular high-protein diets promote protein intakes of 71 to 162g/d, or 28% to 64% of energy, and severely limit carbohydrates to 7 to 56 g/d, or 3% to 16% of energy.

High-protein, high-fat diets induce metabolic ketosis and are initially attractive because they may induce quick weight loss.  This initial weight loss, however, may be attributed in part to the diuretic effect from low carbohydrate intake and its effects on sodium and water loss, glycogen depletion, and ketosis.  As the diet is sustained, loss of appetite associated with ketosis leads to lower total caloric intake.  High-protein diets of >30% kilocalories from protein also can promote negative energy balance due to significant restriction in the type and amount of foods eaten.  The structured eating plan, strict eating schedules, and limited tolerance for high-protein foods reduce overall flexibility but offer initial appeal.  These characteristics may help limit caloric intake and may account for weight loss.  However, neither the efficacy of these diets compared with higher carbohydrate diets in promoting weight loss nor the safety of these diets has been documented in long-term studies.

The amount of protein recommended in high-protein diet regimens exceeds established requirements and may impose significant health risks.  First, animal protein (rather that plant-based proteins that also contain carbohydrates) is generally advocated in these diets.  A diet rich in animal protein, saturated fat, and cholesterol raises low-density lipoprotein (LDL) cholesterol levels, an effect that is compounded when high-carbohydrate, high-fiber plant foods that help lower cholesterol are limited or eliminated.  Furthermore, a high-carbohydrate diet that includes fruit, vegetables, nonfat dairy products, and whole grains has been shown to lower blood pressure, so limitation of these foods may raise blood pressure via associated reductions in potassium, calcium, and magnesium coupled with increased sodium intake.  High-protein foods such as meat, poultry, seafood, eggs, seeds and nuts are high in purines.  Purines are broken down into uric acid, so excess consumption of these foods increases uric acid levels and may cause gout in susceptible individuals.  A surplus of protein in the system also increases urinary calcium loss, which may facilitate osteoporosis.  In addition, elimination or severe restriction of fruit, vegetables, beans, and while grains from the diet may increase cancer risk.  A very-high-protein diet is especially risky for patients with diabetes, because it can speed the progression, even for short lengths of time, of diabetic renal disease.  Finally, because food choices may be severely restricted on high-protein diets, healthful foods such as low-fat milk products, cereals, grains, fruits, and vegetables (which are higher in carbohydrates and contain essential nutrients) are also generally restricted or eliminated.  This can lead to deficiencies in essential vitamins, minerals, and fiber over the long term; these deficiencies can have adverse health effects if they are allowed to persist.  Furthermore, when carbohydrates are severely restricted with high-protein diets, fatigue often occurs when muscle glycogen is depleted during bouts of exercise.  Some popular high-protein/low carbohydrate diets limit carbohydrates to 10 to 20 g/d, which is one fifth of the minimum 100 g/d that is necessary to prevent loss of lean muscle tissue.

A popular premise of high-protein diets is that excess carbohydrate results in elevated insulin levels, which in turn promotes storage of body fat and other metabolic consequences.  To induce weight loss, the high ratio of protein and fat to carbohydrate purportedly promotes metabolic changes that reduce serum insulin levels.  However, in fact, protein intake also stimulates insulin secretion.  Insulin resistance or hyperinsulinaemia is complex and regulated by a number of interacting factors.  It occurs as a result of obesity or excess fat storage and lack of physical activity, and it can be reduced significantly by caloric restriction, weight loss, and exercise.  Changes in caloric balance over wide ranges of fat intake apparently do not influence insulin action in humans.

There are very few long-term studies of high-protein diets.  One randomized dietary intervention study in 65 healthy overweight men and women that compared 2 ad lib diets varying in protein content (12% versus 25% of kilocalories from protein) demonstrated larger weight losses with the higher-protein diet (8.9 kg) versus the lower-protein diet (5.1 kg) over 6 months.  However, another study showed similar weight losses with diets of varying protein and fat composition, which indicates that total energy intake is the most important determinant for weight loss.  The short-term effects of high-protein diets have been appraised mainly in terms of increased weight loss and its associated benefits.  Deleterious effects on cardiovascular disease risk factors were demonstrated in a study of 24 obese individuals who followed the Atkins diet for 3 months, in whom caloric intake declined but LDL cholesterol levels rose despite the weight loss.  Most of the weight loss occurred in the first few weeks, which suggests the combined effects of fluid loss and potential anorectic effects of induced ketosis.

A recent review of the literature regarding the effects of low-carbohydrate (high-protein) diets reported from 1956 to 2000 concluded from 20 published studies that there is a pattern of weight loss that ranges from 2.8 to 12.0 kg within varying time frames and number and type of subjects included.  However, when carbohydrate is restricted, subjects generally reduce their overall intake of calories, and this calorie deficit is related to the weight loss.  These studies raised important questions regarding the long-term effects of these diets on weight maintenance and overall health.  Long-term studies are needed to determine the overall safety and efficacy of high-protein diets.  In particular, benefits and potential risks beyond the initial weight loss observed should be addressed.

             Guidelines for Evaluating High-Protein Diets

 In evaluating high-protein diets, it is important to ensure that eating patterns follow the AHA Dietary Guidelines and incorporate primary prevention strategies for coronary heart disease, such as those outlined by the National Cholesterol Education Program, especially in persons with multiple risk factors, including obesity:

1.  Total protein intake should not be excessive (average 50 to 100 g/d) and should be

     reasonably proportional (=15% of kilocalories per day) to carbohydrate (=55% of

     kilocalories per day) and fat (=30% of kilocalories per day) intake.

2.  Carbohydrates should not be omitted or severely restricted.  A minimum of 100 g

     of carbohydrate per day is recommended to ensure overall nutritional adequacy

     through the provision of a variety of healthful foods.

3.  Selected protein foods should not contribute excess total fat, saturated fat, or

     cholesterol.

4.  The diet should be safely implemented over the long term, ie, it should provide

     adequate nutrients and support dietary compliance with a healthful eating plan to

     prevent increases in disease risk.

Summary

Scientific studies do not demonstrate that high-protein diets without concomitant decreases in caloric intake result in sustained weight loss or improved health.  Most Americans consume more protein than their bodies need.  Extra protein is not used efficiently by the body and may impose a metabolic burden on the kidneys and liver.  High-protein diets may also be associated with increased risk for coronary heart disease due to intakes of saturated fat, cholesterol, and other associated dietary factors.  When diets high in protein are severely limited in carbohydrates, food choices become restrictive, and overall nutrient adequacy and long-term palatability are also of concern.  Successful weight loss occurs most frequently when a nutritionally adequate diet that allows for caloric deficits (=500 kcal/d for each 1 lb lost per week) is tailored according to individual food preferences.  A minimum of 1200 kcal/d for women and 1500 kcal/d for men should be provided.  Total energy deficit has the greatest overall impact on weight reduction, especially when coupled with increased physical activity and behaviour modification to maintain negative energy balance.  Over the long term, diet composition should be consistent with a balanced eating plan that supports weight maintenance and lowers chronic disease risk.