High Protein / Low Carbohydrate Diets
Strength athletes and body-builders have, rightly or wrongly, long been proponents of high-protein, low carbohydrate diets but recently this fad has crossed over into the 'dieting' population. With influential stars like Jennifer Anniston and Geri Halliwell singing the praises of high protein/low carbohydrate diets for fat loss, many people are giving them a go.
Many perpetual dieters are always looking for the extra edge in fat loss - the diet that will help them shift those last few pounds - and, on the face of it, that seems to be what high protein diets offer. With diet plans like 'The Zone' and 'Dr. Atkins Diet Revolution', you are promised rapid, permanent, easy fat loss - what could be better?
However, the books don't quite tell the whole story. This article reveals the facts about high protein/low carbohydrate diets - the positive and negative effects and the suitability for certain population groups.
What Is Protein?
Protein is one of the macro-nutrients obtained from a normal diet - the others being carbohydrate and fat. The main sources of protein in the diet include meat, fish, eggs, milk, cheese, other dairy products, cereals, nuts and pulses. In non-vegetarian diets, two thirds of the average intake is obtained from animal sources with a further quarter from cereal products and most of the remainder from nuts and pulses. For vegetarians, the principal sources tend to be Quorn, soy products, dairy products, cereals, nuts and pulses.
Protein is made up of amino acids and it is these 'building blocks' that protein is broken down into when digested. These are then absorbed and used to make other proteins in the body such as those needed for muscle building. The human body is able to 'make' a certain number of amino acids itself, but others must be gained from the diet - these are known as essential amino acids.
Protein is contained in all animal and plant cells in differing amounts, but the quality of this protein varies. Protein quality can be assessed according to the number of amino acids present in a food and the 'usability' of the protein.
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Foods that contain all of the essential amino acids are of a higher quality than those which are lacking in one or more of these. Animal sources of protein e.g. meat & dairy products contain all essential amino acids whereas plant sources do not.
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The Biological Value (BV) of a food assesses how well and how quickly the body can use the protein contained within it. Foods with a high BV contain more food that the body can absorb, use and retain. Proteins from animal sources have higher BVs than those from plant sources.
What Does Protein Do?
Protein is essential in the diet for various reasons including:
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It is required for growth and repair of body tissues such as muscle
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It plays a critical role in virtually every biological process that takes place in the body
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All enzymes, which are vital for the body's metabolism, are proteins
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Many hormones are proteins
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Muscle contraction is dependent on protein, as is immune protection and the transmission of nerve impulses
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It provides structural support for skin and bone
Protein can also provide a source of energy - 1g of protein provides almost the same amount of energy as 1g carbohydrate (4kcal). Generally, the body uses carbohydrate and fat for energy but, when there is inadequate dietary carbohydrate, protein may be used as an energy source. However, excess dietary fat will be converted to fat and stored in the body.
What Is A High Protein/Low Carbohydrate Diet?
Basically, it's a diet which involves eating as much protein as you like! So, you can eat unrestricted amounts of meat, fish, cheese, yoghurt, eggs and cream etc. However, you have to virtually eliminate carbohydrate, so you are not allowed pasta, rice, bread, potatoes, sugar or high-carbohydrate fruit & veg. Some of the plans do allow you to bring small quantities of these foods back in after certain amounts of time though.
On the Atkins plan, for example, you could eat fried bacon, sausage and eggs for breakfast, a double cheeseburger (without the bun or chips) for lunch and dinner may consist of a small salad (you have to limit this though) with blue cheese dressing and fried chicken. Other examples of meals include baked cheeses, mushrooms stuffed with sausage and mozzarella, meatballs, steak au poivre and roast chicken. But, if you include vegetables with your meals, these much be low-carb e.g. broccoli and green beans.
The Claims
Obviously, the main claim is that of rapid, easy weight loss which is maintainable and can be achieved whilst eating unlimited calories! Sounds good!
The premise is that, by restricting your intake of carbohydrate, you reduce the production of insulin that the body produces. Insulin is released when carbohydrate is eaten, so the more carbs in the diet, the more insulin is released. This hormone is responsible for storing carbohydrate in the body but once the body's carb stores are full, excess dietary carbs are stored as body fat. So, the theory is that you will lose weight as you will not be raising your insulin levels by eliminating carbs meaning that you will be using fat as a fuel rather than storing it.
Eating protein instead of carbohydrate is also said to stave off cravings as high-protein foods are more satiating than high-carbohydrate ones meaning that they keep you fuller for longer. Protein takes longer to digest than carbohydrate and therefore may stabilise blood sugar levels for longer leading to a reduced likelihood of snacking. Other claims that are often made are:
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improved health due to the elimination of the toxins stored in fat cells as you use fat for energy
- improved lipid profiles
- reduced likelihood of high blood pressure
The Evidence
There is absolutely no scientific evidence which finds that weight can be lost in any other way than creating a negative energy balance i.e. eating fewer calories than you expend. Therefore, any diet that claims to allow you to eat unrestricted calories and still lose weight is seriously flawed. Although there is evidence that shows that weight loss will improve conditions which are closely linked to obesity such as hyperinsulinaemia, hyperglycaemia, hyperlipidaemia and hypertension, it also shows that the improvements are achieved with any kind of weight loss, not just that achieved through high-protein diets (BNF, 1999).
There is evidence that a high-protein, low-carb diet does allow more rapid initial weight loss when compared to moderate-carb diets of the same energy content (Skov et al, 1999). However, the problem with this is that the reason for the rapid weight loss is primarily a loss in body water. Due to the low-carb intake, the carbohydrate stored in the body as liver and muscle glycogen is depleted. When carbohydrate is stored in the body, every gram of carbohydrate is stored with three grams of water. Therefore, a reduction in the body's carb stores leads to a reduction in body fluid and hence quite rapid weight loss.
In reality, although dieters will presume that the rapid weight loss occurs due to a loss of body fat, the body fat stores remain virtually untouched. Whilst most people following these diets will experience quick weight loss initially, this will inevitably slow down after a few weeks. Also, many people claim to put most, if not all of the weight back on when they stop the diet. This is because, once you start eating carbs again, the body's stores refill along with the same water content.
Protein diets will 'fill you up' more and they may increase the process of thermogenesis (Mikkelson et al, 2000) so increasing energy expenditure over a 24h period as compared to balanced diets of the same energy content. As a consequence, there is a greater potential for negative energy balance and weight loss. But, the weight loss is not due to raised insulin levels as claimed by the promoters of the diets. There may also be a reduction in lean muscle mass during periods of low-carb intake and low-calorie intake.
The basis of low-carb diets is a severe restriction of carbohydrate which simply causes a net reduction in calorie intake. Low-carb diets are also, by definition, high in protein and fat. This increases the production of ketones, due to increased fat breakdown (see Risks and Side Effects), which suppress hunger and so further contribute to caloric restriction. So, bearing in mind that to lose weight we have to create a calorie deficit, it is clear to see how it is possible to lose weight this way.
Risks & Side Effects
High protein diets may pose a risk to health, so much so that the American Heart Association has issued a warning about them. This warning has been published in their journal, 'Circulation', and basically states that there is no proof that these diets help people to lose weight in the long term. It also warns about risks to health for people who stick to these diets for more than a short period of time. Professor Robert Eckel, who co-wrote the advice said,
"High protein items [of food] may also be high in fat. Some of the diets increase fat intake and reduce nutritionally rich foods such as fruit & vegetables, which is not a good approach to meeting a person's long-term dietary needs. Many of these diets fail to provide essential vitamins, minerals, fibre and other nutritional elements, in addition to their high fat content."
When consuming extremely low levels of carbohydrate (<100g per day), high levels of 'ketones' are produced leading to an abnormal metabolic state called 'ketosis'. Ketones are chemicals which are produced when fatty acids are used as fuels due to their being insufficient carbohydrate stored in the liver and muscles for the body to use. In times of starvation, ketones are used as a fuel by the brain and heart muscle to keep us alive. However, the presence of ketones in the body leads to an increased loss of sodium and body water, bad breath, taste changes, nausea, constipation, headaches, fatigue and dizziness.
Too much protein in the diet can also tax the kidneys which have to work harder to process and excrete the nitrogen contained in protein. If high-protein diets are continued over a long period of time, this could lead to permanent kidney damage.
Due to the reduced carbohydrate intake, less fibrous starch, dietary fibre and vitamins & minerals are consumed. These factors significantly increase the risk of cardiovascular disease, renal disease, cancers and bowl disorders. High-protein diets are therefore even less suited to people who already have an increased risk of these diseases.
Additionally, due to the amount of fat being consumed, the risk of coronary heart disease may be increased as the saturated fat and cholesterol content of the diet is vastly higher.
Also, this type of diet is becoming a 'special occasion' diet whereby people use it for rapid weight loss in minimal time sporadically throughout the year. This can lead to weight cycling which has been identified in its own right as a risk factor for cardiovascular disease.
High-protein diets have been shown to be low in calcium content due to the low calorie intake, as more orthodox weight loss regimes. However, ketogenic diets may also lead to increased calcium excretion and reduced bone mineral density (Willi et al, 1998). Although the evidence concerning the effects of this on the risk of developing osteoporosis in later life is insufficient at present to be able to draw firm conclusions, it is very likely that it will have a negative effect.
Gout is another potential problem as the amount of uric acid in the blood increases due to the fact that it must compete with the ketones in order to be excreted. This increased level of uric acid in the blood can also add to the increased risk of kidney problems.
People following high-protein diets may also experience mood changes such as increased tension and irritability which may result in cravings for high-carb foods and fatty snacks. These mood changes are opposite to those experienced when following high-carb diets. Consuming carbohydrate causes the release of serotonin - the feel good brain hormone - thus improving mood and appetite. In fact, it is known that high-carb dieters have fewer cravings and better overall moods than those on high-protein plans.
Summary & Conclusions
No medical or scientific body recommends high-protein diet plans, in fact most will advise against them and these types of diets are certainly not a magic solution to fat reduction. Evidence shows that high-protein/low-carb diets are no more successful than regimes recommended by the scientific and medical communities i.e. low-fat, moderate-carbohydrate and moderate-protein combined with a physical activity programme.
These diets are more dangerous than others for various reasons, as already mentioned. Therefore people wishing to follow them should check with their GP beforehand and regularly throughout to monitor their cholesterol levels and other heart disease risk factors. However, there has been no research into the short-term use of ketogenic diets in relation to health problems, so there may well be benefits of short-term use which outweigh any potential risk factors.
The evidence for the use of low-fat, moderate-protein and moderate-carbohydrate diets for effective, consistent weight reduction, on the other hand, is vast (Robson, 2001) and when combined with a sensible physical activity regime, the results are even more positive.
References
British Nutrition Foundation (1999). Obesity. The report of the British Nutrition Foundation Task Force. Blackwell Science.
Skov, AR et al (1999). Randomised trial on protein Vs carbohydrate in ad libitum fat reduced diet for the treatment of obesity. In J Obesity, 23(5), 528-536.
Mikkelson et al (2000). Effect of fat reduced diets on 24-h energy expenditure: comparisons between animal protein, vegetable protein and carbohydrate. Am J Clin Nutr, 72(5), 1135-1141.
Robson (2001). High protein, low carbohydrate diets for weight loss: clarifying the evidence. Dietetics Today, 36(9), 13-15.
Willi et al (1998). The effects of a high protein, low fat, ketogenic diet on adolescents with morbid obesity: body composition, blood chemistries and sleep abnormalities. Paediatrics, 101(11), 61-67.