Low-carb diets have been popular in the Western world for some time; by nature they focus on reducing the amount of carbohydrate in the diet to promote weight loss.
Many people think of the low-carb diet as a "fad diet", but it shows little sign of falling out of favour, having become very popular as the Atkins diet in the early 1970's. Recent forms of the low-carb diet include the "new" Atkins diet, the Zone diet and the Paleo diet which are fairly similar in their basis.
Low-carb diets usually restrict carbohydrates to less than 20% of energy intake. These diets are not just low in carbs - they are also high in protein and often also fat. Studies have shown that this approach can help some people to lose weight in the short terms, and this is probably because the protein helps to keep you feeling full, which can help appetite control. For example, a study published in the New England Journal of Medicine found that people who ate a low-carb diet lost more weight than those receiving a conventional "low-fat" diet for the first six month. There have now been a number of trials, mostly in people with health problems, including those who are obese or have type 2 diabetes, and the majority have shown the low-carb diet to do better than a low-fat diet at the beginning.
Although longer-term studies are more limited, those that have compared weight loss on calorie controlled low-carb and low-fat diets over at least a year have generally found little difference between them. In other words, different weight-loss strategies are effective in different people, particularly over a prolonged period of time. Concerns also remain about the safety of this type of dietary pattern in the long term. Cutting out a whole food group may result in a diet that does not contain all the nutrients the body needs, for instance, especially since cutting carbs inevitably leads to a low fibre intake, which can have an adverse effect on gut health. Eating high-fat foods may lead to a high intake of saturated fat, which is linked to increased risk of heart disease.
The high animal protein content of many of these types of diets is also at odds with current advice to consume more sustainable sources of protein, like beans, lentils, pulses, nuts and Quorn. So most experts agree that low-carb diets should, if anything, be considered as a temporary weight-loss tool rather than a "diet for life". Carbohydrate is an important source of energy for the human body - which is why low-carb diets can sometimes lead to headaches and fatigue - but starchy foods are not fattening per se.
Weight gain typically results from eating more calories than your body uses, and these calories can be from any source - protein, fat, carbohydrate or alcohol. (Carbohydrate contains 4kcal/g compared to fat, which contains 9kcal/g; 1g = 0.035oz). However, starchy foods are sometimes combined with high-fat ingredients e.g. butter on bread or creamy sauces with pasta, and this makes them much higher in calories. But provided starchy foods are not cooked or served with a lot of fat, and portion sizes are moderate, they are relatively low in calories.
Low-carb diets and type 2 diabetes
SACN concluded that the proportion of carbohydrates in the diet has no effect on the risk of developing type 2 diabetes. But there has been a lot of interest in the role of low-carb in managing type 3 diabetes. The amount, type and frequency of carbohydrate-containing foods in a diet is very important for blood glucose management, and including low-glycemic-index (GI) carbohydrate foods within a healthy, balanced diet can be a strategy to help them with blood sugar control. And because 90% of people with type 2 diabetes are obese or overweight, low-carb diets can also aid weight loss.
Nonetheless, the experts suggest that while low-carb diets can help some people, there is no consistent evidence that they have any advantage over other diets in the long term (Diabetes UK, 2016). Many diets that include low-carbohydrate, Mediterranean, low-fat or very low-calorie foods can help people lose or manage their weight, and the choice should be based on individual food preferences and lifestyles - whats most important is being able to stick to the diet over a long period. Before making any dietary changes to reduce carbohydrate intake, people with type 2 diabetes should always seek medical advice, as dietary changes may require alterations to medication.
The bottom line: The main reason why a low-carb diet may be effective for weight loss seems to be related to the relatively high protein content of these diets rather than the lack of carbohydrate. So rather than focusing on cutting out carbohydrates if you are trying to lose weight, it is a better idea to include, protein-rich foods like lean meats, skinless chicken, fish, low-fat dairy products and pulses in your main meals. Including wholegrain carbohydrate foods will also provide more fibre, which can be helpful for weight loss, too.
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