The term low carb diet is a broad term for popular diets (Such as Atkins, South Beach The CHO Addict’s Diet, Protein Power Diet, Sugar Busters Diet) that restrict carbohydrate intake (pasta, bread, potatoes, rice, cereals and sugary foods and drinks). They typically contain less that 100g carbohydrate per day. These foods in the diet are replaced with foods containing high percentage of proteins and fats (meat, poultry, fish, eggs, cheese and nuts). These diets are aimed at helping individuals to lose weight, treat obesity or other conditions such as diabetes and metabolic syndrome. When dietary carbohydrate is restricted the body begins to break down fat stores in order to meet energy requirements. When fatty acids are broken down they produce various chemicals called ketones, which are present in the blood, urine and breath, a process known as ‘ketosis’. It is generally been theorised that diets containing high levels of refined carbohydrates may have contributed to epidemic levels of many disease of modern society such as type 2 diabetes and metabolic syndrome.
During the early 19th century, these diets ‘ketogenic diets’ were used to treat diabetic patients. They became fashionable again in the 60’s and then in 1972 Atkins released his book ‘The Dr Atkins Diet Revolution’. He used the low carbohydrate, high protein diet to treat his patients and was criticised by the mainstream medical profession for the diet being potentially dangerous and misleading, due to the diet not restricting fat (saturated fat) together with the potential harm of causing ketosis in the early stages of the diet. He published another book in the 1990’s that started off another ‘low carbohydrate diet’ craze, which spread across America and the UK. The low carbohydrate diet appeared to lose popularity by the end of the 2000’s. Today, there are different approaches to low-carb diets. Generally they tend to advocate the elimination of refined sugars and highly process cereals (white bread) from the diet.
Low-carb diets have a higher percentage of dietary energy derived from protein containing foods that are known to help satiety. Weight loss is probably due to a daily reduction in calorie intake through a reduced appetite. Also low-carb diet made up of low GI carbohydrate foods can reduce the insulin response, a hormone that helps to control blood sugar levels. This is thought to help improve glycaemic control (blood sugar levels) in diabetic patients. Reduced insulin levels may also help to reduce fat storage and weight control. There is some evidence that ketones produced during ‘ketosis’ may help to suppress appetite, which could account for the rapid weight loss often associated with low-carb diets. However, there is concern that ketosis can affect calcium metabolism, and in the long-term could increase the risk of kidney stones and osteoporosis.
These diets have been shown to be effective in initial weight loss. Although, the initial weight loss in the early stages comes from loss of glycogen (carbohydrate stores), water and muscle rather than predominantly fat reserves. During weight loss strategies ideally we want to preserve the muscle tissues to support our metabolism to help burn calories. If you lose muscle you will reduce the amount of calories you need each day, which means you have to work harder to keep your weight under control. There is no evidence to show these diets are effective in long-term weight management.
Generally the medical, dietetic and nutritional scientific professionals have opposed, or voiced caution for low carbohydrate diets. If these diets are very restricted in carbohydrates it leads to ‘ketosis’ that can cause symptoms of headache, bad breath, fatigue, reduced exercise tolerance and mood. Low-carbohydrate diets tend to be higher in fat, and eating a high fat diet (especially one rich in saturated fat from foods such as meat, cheese, cream and butter) could increase the chances of developing heart disease. Low- carbohydrate diets may also restrict the amount of fruit, vegetables, whole grain products reducing overall intake of dietary fibre, vitamins, calcium, potassium, magnesium and iron. All of which are vital for good health. The jury is still out on how safe and effective a low-carb diet is especially in terms of long-term weight management. The Food standards Agency are concerned with regard to the high fat content of these diets. The American Heart Association doesn’t recommend high protein diets due to their associated risk for coronary heart disease. The British heart foundation study of low-carbohydrate diets found negative effects on the heart commenting ‘we would certainly not recommend high-fat low-carb diets to anyone who wants to lose weight and look after their heart’. The American Dietetic Association have discussed acceptance of carbohydrate-controlled diets as effective treatment for short-term (up to one year) weight loss in obese patients suffering type 2 diabetes.
There is no long-term data on the efficacy and safety of low-carb diets. There is some evidence to suggest some favorable cardiovascular effects, such as reductions in insulin, glucose, blood pressure and blood triglycerides, but also negative effects on other cardiovascular risks. Low-carb diets can increase the loss of muscle making it more difficult to control weight. Therefore, low-carb diets do not appear to offer any clear advantage over calorie restricted diets with regard to long-term weight control. However, they may be an effective treatment in a short-term weight loss programme for obese patients with type 2 diabetes.