EFFECTS OF DIET ON CORONARY BLOOD FLOW
Is a High Protein Diet Healthy?*
The Atkins Diet, the Zone Diet and the Scarsdale Diet all have in common:
- High protein
- Low carbohydrate.
High protein, low carbohydrate intake has been routinely used for the past 40 years for weight reduction.
What is Protein?
Proteins are large biological molecules consisting of one or more chains of amino acids. Proteins differ from one another primarily in their sequence of amino acids.
Amino acids are biologically important organic compounds made from amine (-NH2) and carboxylic acid (-COOH) functional groups, along with a side-chain specific to each amino acid. The key elements of an amino acid are carbon, hydrogen, oxygen and nitrogen as well as other elements found in the side-chains. There are 23 proteinogenic ("protein building") amino acids that combine into peptide chains (polypeptides), which are the building blocks of the vast array of proteins. 20 of these 23 proteinogenic amino acids are known as "standard" amino acids and of these, 9 are “essential”.
An essential amino acid is an amino acid that cannot be synthesised de novo by humans and therefore must be supplied in the diet.
After the amino acids, and in particular the 9 essential ones, were identified, proteins were divided into first and second class proteins.
First class proteins are ones which contain all essential amino acids in required proportions by the human body. ‘First class’ proteins are typically found in all meats, and, for example, egg albumin.
Second class proteins contain only some of the essential proteins, although generally no more than one or two are missing. Vegetable proteins are generally labelled 'second class'.
It is now accepted that this classification of first and second class proteins is flawed. First class protein was supposed to be of greater nutritional value. Hence protein from animal sources was 'good' for you, whereas plant protein, being second class was inferior. In actual fact, this classification of first and second class protein has NO validity in the diet as a whole. The amino acid lacking in one plant protein is present in the protein from another plant/vegetable/fruit etc.
Recommended Daily Intake of Protein
The recommended daily intake of protein for Australians is:
Adult males age 19-70 years
64g/day or 0.84g/kg
Adult males age >70 years:
81g/day or 1.07g/kg
Adult females age 19-70 years
46g/day or 0.75g/kg
Adult females age >70 years
57g/day or 0.94g/kg.
(Nutritional Reference Values for Australia and New Zealand, www.nhmrc.gov.au)
Examples of High Protein Diets
Dr Robert Atkins first published his book Dr Atkins Diet Revolution in 1972. It is essentially a high protein, high fat, low carbohydrate diet, a diet that results in ketosis, ie it is a ketogenic diet. Ketosis is a condition in which levels of ketones in the blood are elevated. Ketones are formed when glycogen (glucose) stores in the liver have been depleted. They are used for energy and are created by the breakdown of fat stores.
The Atkins diet is discussed, and condemned, in my December 2011 newsletter 2012 - How Healthy will You be?. Initially, a maximum of 60 grams of carbohydrate (240 calories) is permitted, the rest of the diet is protein and fat. On a 2000 calorie/day intake, 1760 calories come from protein and fat.
Dr Barry Sears, in 1995, published his book The Zone. A Dietary Road Map. It is also a high protein ketogenic diet. 40:30:30 are the recommended ratios for calorie/joules from carbohydrate, protein and fats respectively. On a 2000 calorie/day intake, 800 calories from protein (40%) is an intake of 200 grams of protein.
The Scarsdale diet was first published by Dr Herman Tarnower in 1978, The Complete Scarsdale Medical Diet. (Dr Tarnower's clinic was in the town of Scarsdale). It is a very specific and structured diet, to be followed strictly for 14 days initially. It is high protein and low fat. It claims to be "The World's Best Selling Diet Book". The recommended ratios of calorie/joules from protein, fat and carbohydrate are 43%, 22.5% and 34.5% respectively, for the diet to be ketogenic. On a 2000 calorie/day intake, 860 calories from protein (43%) is an intake of 215 grams of protein.
Comparing these figures to the Recommended Daily Intake of protein given above, it can clearly be seen that the Atkins, Zone and Scarsdale diets are HIGH protein diets.
How Healthy are High Protein Diets?
Dr Richard M. Fleming, cardiologist and president of the Fleming Heart and Health Institute, published the following paper: The effect of high-protein diets on coronary blood flow in the journal Angiology, the Journal of Vascular Diseases (2000 Oct; 51(10): 817-826). In this paper, he reported his extensive clinical research on the effects of diets on coronary blood flow.
The background for the study, as set out in the abstract, is as follows: "Recent research has demonstrated that successful simultaneous treatment of multiple risk factors [listed in detail] can lead to the regression of coronary artery disease and the recovery of viable myocardium. However, preliminary work revealed that a number of individuals enrolled in the original study went on popular high-protein diets in an effort to lose weight. Despite increasing numbers of individuals following high-protein diets, little or no information is currently available regarding the effect of these diets on coronary artery disease and coronary blood flow."
A prospective one year study was carried out.
26 people were studied for one year by using myocardial perfusion imaging (MPI), echocardiography (ECHO), and serial blood work, to evaluate the extent of changes in regional blood flow, regional wall motion abnormalities, and several independent variables known to be important in the development and progression of coronary artery disease. In addition, single-photon emission computed tomography (SPECT) imaging was used to look for coronary artery disease (CAD) and regional cardiac wall motion abnormalities. The extent and severity of perfusion and blood flow through each of the coronary beds was determined quantitatively according to established protocol.
Each of the multiple risk factors for heart disease [as listed], was independently treated as previously reported. MPI, ECHO and SPECT were performed at the beginning and at the end of the study for each individual.
The "treatment group" TG comprised 16 people who modified their diet as instructed. This was a very low fat diet, with fat suppling only 15% of calories, and very high in complex carbohydrates (mostly unrefined), and low in protein. This was the "low fat" or LF Diet.
10 additional individuals elected to follow a different dietary regime consisting of a "high protein" diet, the HP Diet, which they believed would "improve" their overall health.
|Changes in Extent and Severity of Coronary Artery Disease|
|Total Coronary Artery Disease||Total Coronary Artery Disease|
|Low Fat (LF) Diet||-22.9||-21.8|
|High Protein (HP) Diet||+39.7||+52.0|
The "Total Coronary Artery Disease" was the cumulative data from the measurements of the various branches of the coronary arteries such as the left anterior descending, left circumflex etc.
It can be clearly seen that the total overall effect of the Low Fat, LF group was 22.9% regression in the extent of CAD and a 21.8% reduction in the total severity of CAD. In sharp contrast, the total overall effect seen in the High Protein, HP group was 39.7% progression in the extent of the CAD and a 52.0% worsening in the severity of the disease.
Also, individuals in the HP group showed worsening of their independent variables. Most notably, fibrinogen (a clotting factor), lipoprotein (a) and C-reactive protein (a measure of inflammation) increased by an average of 14%, 106% and 61% respectively. These results would suggest that the high protein diets may precipitate progression of CAD through increases in lipid deposition and inflammatory and coagulation pathways.
Problems with Meat-based Diets for Diabetics
High-protein, animal-based diets in diabetics are the result of the recommendation to limit the intake of refined grains and simple sugars. The logic here is that if sugar and refined grains and other high-glycemic foods raise blood sugar and triglycerides, more protein instead of carbohydrates should be consumed.
Carbohydrate-restricted diets rich in animal products, i.e. high-protein diets, offer some short term benefit with improvement in glucose control and weight loss. However, the problem is that the increased protein intake promotes the progression of diabetic kidney disease, and the higher saturated fat intake raises cholesterol and, as shown above, promotes heart disease.
This worsening of diabetes from increased animal product consumption was borne out in a recent study in which researchers analysed the diets of 38,094 participants in The European Prospective Investigation into Cancer and Nutrition Study. It was found that for every 5% of calories consumed from animal protein, the risk of diabetes increased by 30%. Increased animal protein intake also coincided with increased body mass index, waist circumference and blood pressure. Vegetable protein was not associated with increased diabetes risk.
In view of the heavy marketing of these high meat and animal protein diets for weight loss and the treatment of conditions like diabetes, and their popularity, the clinical findings as detailed above are particularly disturbing and alarming. Dr Joel Fuhrman, in his book The End of Diabetes (2012), referring to "physician-recommended high-protein diets" says "I consider this advice malpractice."
The diet as detailed in my March 2009 newsletter Foods for Health is one which is dominantly vegetarian, with a high nutrient density content, high in fibre, low in both protein and fat. It is recommended as the ideal healthy diet and avoids the problems that result from eating so many animal products.
*Copyright 2013: The Huntly Centre.
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