High-protein diets are hot news, attracting millions of dieters and considerable controversy in the media. Will increasing the protein level in your diet lead to lasting fat loss, without compromising your health? In the first of this two-part series, I review the weight loss evidence in this epic nutrition debate.

The major benefit of protein in a fat loss diet appears to relate to the enhancement of satiety, curbing of hunger and resulting reduction in energy consumption. But this aspect has only been recently promoted. To understand the protein story fully and be able to relate it to clients, it's helpful to know the early chapters of this ongoing nutrition issue.

When Dr Robert Atkins published the “Dr. Atkins Diet Revolution” in 1972 it became a best seller, despite its radical formulation that defied medical authorities. His eating plan cut carbohydrate intake down to 20g per day in the initial phase and substantially elevated dietary protein.

Atkins' major claim was that dramatically reducing carbohydrate puts your body into a state of ketosis, the biological starvation mode that causes rapid mobilisation of body fat stores for energy. The potential appetite suppressing affects of protein didn't appear to be recognised by Atkins or at least they were not promoted well.

Atkins' diet was met with immediate condemnation from health authorities, who correctly judged it to be deficient in the key vitamins, minerals and fibre that are provided by complex carbohydrate foods.

Perhaps the greatest concern though, was the high fat level in Atkins' diet. In the early 1970's health authorities had only really just started broadcasting warning messages about saturated fat and its strong link with high blood cholesterol levels and heart disease. The Atkins Diet, seemingly full of bacon, eggs and steak was so counter to healthy eating that it never had a chance, nor should it have of becoming a recommended dietary option for weight loss.

Over time, Atkin's supporters abandoned him in favour of low fat diets widely promoted and accepted for both enhancing weight loss and reducing coronary heart disease risk.

Enter the Zone

Despite the focus on cutting dietary fat in the 1990's, carbohydrate continued to receive its share of negative press. When Dr Barry Sears released “Enter The Zone” in 1995, it offered dieters a less severe carbohydrate restriction. The Zone promoted a strict dietary ratio of 30% fat, 40% carbohydrate and 30% protein. It's success was short lived, not only because `Zoners' found it difficult to adhere to the exact macronutrient ratio, but due to criticism of Sears for a number of technical errors in his book relating to nutritional biochemistry. Without the support of academics and health authorities The Zone zoned out, like many diet fads. Similar to Atkins, the role of protein in reducing appetite took a back seat to a more complicated and confusing biochemical explanation for Sears' diet.

Return of Atkins

By the end of the 1990's low fat diets had failed to deliver on their slimming promises, at least in the public's eye. Obesity rates continued to escalate, giving Atkins the opportunity to make a come back, by once again targeting carbohydrate as the culprit. In 2001 the “Dr. Atkins' New Diet Revolution” was unleashed on a new generation of slimmers.

The diet was subsequently reformulated to limit saturated fats and recommend monounsaturated fats such as olive oil. Unlike three decades previous, there was now a larger and more readily available range of low-fat, high-protein foods, including lean meats, low-fat daily products and of course protein bars and shakes.

All these factors and increased awareness of Atkins, now driven by internet promotion and digital “word of mouse” attracted enough interest from nutritional scientists to put the diet to the test. Until then, there had been little quality research examining low-carbohydrate, high-protein diets for weight loss. Even so, the new Atkins' diet was still too low in carbohydrate to be a healthy option.

The research reveals

In 2003, the first two new studies comparing low-carbohydrate, high-protein diets over six and twelve months were published in the New England Journal of Medicine. Both studies found that subjects lost considerably more weight at six months eating Atkins-type diets versus more conventional weight loss diets. However, the twelve month study found at the end that subjects lost almost identical amounts of weight.

Although trophied as proof Atkins worked, these studies had relatively few subjects and had a high dropout rate which limited the findings. It was also unknown how much fat versus muscle subjects lost. A 2004 six-month study did however find significantly less lean muscle loss on an Atkins-type diet.

Since then, other studies have revealed similar outcomes -- better initial weight loss at six months or less on a low-carbohydrate, high-protein diet , but little if any difference in weight loss over longer periods when compared to a diet of the same total energy, but with recommended levels of carbohydrate and protein.

Although mentioned, few of these studies directly addressed the role of protein in appetite suppression, particularly in the initial stages of a diet. Most researchers were quick to point out that it is daily energy restriction and not specific proportions of macronutrients that is paramount for lasting weight loss.

Protein and appetite

The July 2005 issue the American Journal of Clinical Nutrition (AJCN) shined the spotlight on protein and appetite. Researchers at the University of Washington showed that an increase in protein from 15% to 30% of energy and a reduction in fat from 35% to 20%, at a constant carbohydrate intake, resulted in a spontaneous drop in average daily energy consumption of 441 Cal.

A Big Mac has around 500 Cal, so this figure is substantial. Subjects had higher ratings of satiety and lower ratings of hunger on the higher-protein diet.

This is not the first study to show reduced energy intake with a higher-protein diet, but it will be a strong stimulus more research in this area. The Washington team could only speculate why protein produced greater satiety and that it may relate to complex hormonal systems involving leptin, which is produced by fat cells.

In the journal's editorial, Professor Arne Astrup from Denmark commented, “The problem nowadays is that many people are extremely sedentary, which makes it possible to overeat even when dietary intakes are relatively small… This is why the current focus of science is to increase the satiating power of the diet, so that people feel full with fewer calories.”

High protein and health

Feeling full with fewer calories is a simple dietary proposition and one where protein may have always had its greatest use in fat loss diets. However questions still remain about how to improve adherence to higher-protein diets. And more importantly, about the long-term health impact of such diets.

Most of the controversy over higher-protein diets surrounds the potentially negative impact on heart and bowel health. Current recommendations for red meat consumption are 3-4 serves a week and some diets recommend greater amounts. Questions also remain regarding the effects of raising protein on kidney function and bone status.

Read more about protein and weight loss:
Protein - What about the health risks?
CSIRO Total Wellbeing Diet Review
Interview with Dr Manny Noakes, CSIRO

Matt O'Neill - Copyright 2005

Top | Subscribe | Send to a friend