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Weight loss and carbohydrates
Carbohydrates are the only fuel source for many vital organs, including the brain, central nervous system and kidneys. The digestive system breaks down carbohydrates into glucose and the pancreas secretes a hormone called insulin to help the glucose move from the blood into the cells.

Very low carbohydrate diets
Very low carbohydrate diets are becoming popular again. These diets often contain less than 60g of carbohydrate per day. Many health professionals do not support these diets because they have a high fat content (particularly saturated fat) and restrict fruit, vegetables and high fibre breads and cereals.

Low carb diets restrict healthy food choices
Advocates of very low carbohydrate diets advise people to consume kilojoules mainly from protein and fat sources. This means limiting cereals, some vegetables and fruit, while eating more meat, dairy foods and fat. Typical foods eaten on a low carbohydrate diet include beef, chicken, bacon, fish, eggs and non-starchy vegetables, as well as fats such as oils, butter and mayonnaise. Forbidden foods include fruit, bread, grains, starchy vegetables and dairy products other than cheese, cream or butter.

Very low carbohydrate diets do not meet your daily nutritional needs. To be healthy, your daily diet should include at least:
• Four serves of bread or cereals
• Two serves of fruit
• Five serves of vegetables
• Two cups of milk.
The long term safety of a diet very low in carbohydrates but high in saturated fat is still uncertain. Some experts believe it’s a recipe for a heart attack. Follow-up studies are needed over years to determine the safety of very low carbohydrate diets.

Weight gain comes from eating too many calories
The basic principle of any low carbohydrate diet is that carbohydrates cause weight gain. This is misleading. You gain weight if you consume too many kilojoules (or calories) - it doesn’t matter whether they are from carbohydrates, proteins or fats.

There’s nothing special about a low carbohydrate diet
Low carbohydrate diets cause you to lose weight because they restrict kilojoules or energy. This approach to eating starves the body of the nutrients it needs and can cause major metabolic disturbances to the body. There is nothing special about the proportions of protein to carbohydrate - there are just fewer kilojoules consumed in these diets, which causes the weight loss.

Low carb weight loss is mainly water in the short term
The body stores excess glucose as glycogen and converts glycogen back into glucose to use as fuel if there is not enough carbohydrate in the diet. Around 3g of water is needed to release one gram of glycogen, so the rapid initial weight loss on a low carbohydrate diet is mostly water, not body fat.

When a normal diet is resumed, some muscle tissue is rebuilt, water is restored and weight quickly returns, mostly as fat. This can contribute to the problem effect of dieting called the ‘yoyo’ effect.

Weight loss needs a healthy approach
A diet high in fruits and vegetables, wholegrains, legumes and low fat dairy products, and moderate in fat and kilojoules, is the best way to lose weight and keep it off.

Vegetarians and people who consume predominantly plant-based diets are generally slimmer and have much lower rates of obesity, heart disease and cancer than people who eat meat-based diets. This supports current thinking that diets high in unrefined carbohydrates help to prevent overweight and obesity.

Short term side effects of low carbohydrate diets
Within a short period of time, the effects of a very low carbohydrate diet include:
• Nausea
• Dizziness
• Constipation
• Lethargy
• Dehydration
• Bad breath
• Loss of appetite.
Potential long term effects of low carbohydrate diets
The potential effects on health if a very low carbohydrate diet is consumed long term are unknown. However, these diets may be nutritionally inadequate because they contain few fruits and vegetables. They tend to be low in fibre, thiamin, folate, vitamins A, E and B6, calcium, magnesium, iron, potassium and antioxidant phytochemicals. Such a diet could increase a person’s risk of developing cancer by restricting intakes of antioxidants and fibre from fruits and vegetables.

Very low carbohydrate diets also tend to be high in saturated fat which can contribute to heart disease risk. Diets that are high in protein and fats are associated with abdominal obesity and obesity-related disorders including heart disease, diabetes and cancer.

If the body doesn’t receive enough carbohydrate, it breaks down muscle and other tissue to produce glucose. This causes a build-up of waste products called ‘ketones’. This state, known as ‘ketosis’, is commonly seen in people who are starving, suffering from anorexia nervosa or with untreated insulin-dependent diabetes. Ketones make the blood acidic. Ketosis can be fatal in severe conditions, particularly for pregnant women, their unborn babies and for people with diabetes. There is also evidence that the heart may not be able to function to its full capacity when ketone bodies are its main source of fuel.

A very high protein diet can be dangerous
High protein foods, such as meat, are usually high in saturated fats and cholesterol. Typically these high protein diets contain about 125g protein per day and moderate amounts of carbohydrate. The long term health risks of a diet high in protein include:
• High cholesterol, which is associated with a range of conditions including heart disease
• Increased risk of developing gout and gall bladder colic
• Kidney problems in people with impaired kidney function or diabetes
• Liver problems
• Loss of bone mineral content.
Select carbohydrates, proteins and fats carefully
If you do choose to follow a low carbohydrate diet, do not avoid carbohydrates completely - you need some in your diet to metabolise fat. Choose carbohydrate rich foods that are unrefined or unprocessed, including whole grains and fruit, rather than the more refined and energy-dense forms such as cakes, sweets and soft drinks. Have a variety of vegetables daily.

Select a variety of protein rich foods that are also low in saturated fat, for example:
• Lean cuts of red meat
• Fish (including fatty fish)
• Lean chicken and pork.
You could also select protein rich foods that are plant-based, for example:
• Nuts
• Legumes such as beans and pulses
• Soy products, including tofu.
Choose fats from plant sources (such as olives, olive oil, canola oil, peanuts, peanut oil, soy or soy oil) rather than from animal sources (butter or meat fat).

Ultimately, to avoid weight gain, energy intake should not be more than energy output over a period of time. Avoiding large portion sizes will help keep energy intake in check. For long term weight management, the benefits of regular physical activity cannot be emphasised enough.

Where to get help
• Your doctor
• Accredited practising dietitian (APD).
Things to remember
• Carbohydrates are essential for a healthy body and should not be removed from the diet.
• A very low carbohydrate diet combined with very high protein intake is not recommended.
• Very low carbohydrate diets tend not to lead to long term weight loss.

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