Low Carb Diets

Low carbohydrate diets been around for a long time but recent publicity has sparked renewed interest.  Do they work? Are they safe? Can you lose weight?  Read dietitian Lyndel Costain’s verdict on the latest low carb diet research.

What Are Low Carbohydrate Diets?

There is no clear definition of a ‘low carb diet’.  In fact, different popular diets and research studies described as ‘low carbohyrate’ can vary greatly in their carbohydrate content.  This means not all low carb diet plans are the same.

For example, those with a very low carbohydrate content, such as the first phase of the Atkins diet, are based on the premise that a diet very low in carbohydrate leads to a reduction in insulin production and forces the body to use fat stores as its main fuel/energy source.

When this happens the body produces ketone bodies to fuel parts of the body such as the brain and red blood cells that can’t use fat for fuel (they normally rely on carbohydrate). This leads to ketosis - characterised by smelly breath (an acetone smell like nail varnish) and possible side effects such as headaches and dizziness.

What's Involved?

Permitted foods can vary but basically each low carb meal would include a good-sized protein serving e.g. meat, chicken, fish, eggs, cheese plus low carb vegetables/salad, plus moderate amounts of oil or butter.

A typical day may include a cheese omelette or eggs and bacon for breakfast, a chicken salad with a low-carb salad dressing for lunch, grilled salmon with green vegetables or salad for dinner, and half an avocado, olives, some nuts, and cheese as snacks plus plenty of sugar-free drinks over the day.

Diets which are lower in carbs than a usual balanced diet but not to the extent that they lead to ketosis, typically include measured amounts of fruit, yogurt/milk, starchy veg, pulses or wholegrains e.g. porridge, rye bread, whole wheat pasta.

Popular diet examples include the Zone Diet and the CSIRO diet.  Diets which start off with a very low carb content add such foods back in controlled amounts over time e.g. Atkins and the Dukan diet.

Do Low Carbohydrate Diets Work?

In the short term, most people who go on low carb diets do lose weight and they can lose it very quickly, especially if it is very low in carbs. However, much of the initial weight loss comes from loss of fluid, not body fat.

When our carbohydrate intake is slashed we use up carb stores in our liver and muscles (known as glycogen).  Glycogen is stored with 3 times its weight in water meaning that 7lb weight losses are possible from fluid alone in the first week.  Weight loss is also down to eating fewer calories. 

There is no magic here – nor does ketosis offer any special fat-burning properties. As with any ‘diet’, no matter how weird or sensible, true fat loss only happens if the diet’s guidelines cause you to eat fewer calories than you burn.

When low carb diet intakes have been analysed, on average, people are eating around 1500-1600 calories a day.  Which is why, after the initial fluid loss, weight loss continues at a steadier rate. Low carb diets also tend to have a higher protein content, and protein may help people feel fuller for longer.

When it comes to research studies, evidence suggests lower carb diets can be as effective – no better/no worse - as other dietary approaches over 2 years. But those with strict food rules can be hard to maintain. Interestingly, those with a more moderate carbohydrate restriction can be easier to keep up and as effective as lower carb diets.

Can Low Carb Diets be Healthy?

They can be, depending on the approach used.  Very low carb diets are typically low in fibre (constipation is common), and a multivitamin and mineral supplement is recommended.

Any diet which over-restricts nutritious and fibre-rich foods such as wholegrains, root vegetables and pulses, and promotes a high saturated fat intake is not in line with sustainable and healthy eating recommendations.

When people lose weight, by whatever means, including low carb diets, they usually get health improvements such as lower blood pressure, better insulin and blood sugar regulation and cholesterol levels.

Shorter-term studies haven’t found negative effects of low carb diets on people’s kidneys– but they are not advised for people who already have kidney problems.  There is still a question mark over the long-term healthiness of true low carb diets since some large studies have found a link between low carb intakes and higher mortality (death) rates.  More research is needed to clarify these links.

The Bottom Line

Different dietary approaches suit different people, and new approaches can be motivating, at least initially. Studies comparing different types of diets found that the most effective ones didn’t relate to their carb or protein content, but how well people were able to keep to them – no surprise really!

A low carb diet, or any dietary approach is only effective if it is nutritionally sound, helps you to consume fewer calories than you burn, and can be kept up.

Key elements for success include:

• A food diary of some type,
• having planned times for your meal and activity pattern,
• learning what’s in food
• getting support

 

Also, developing the skills to stay on top of unhelpful thoughts or triggers such as ‘all or nothing’ thinking or stress/comfort eating.

If you are interested in a lower carb approach it’s wise to discuss it with your GP or other health professional, especially if you have any health problems or are taking any medication. If you do your own thing or choose to use a popular diet opt for approaches which encourage healthier fats, lean meats, fish, plenty of veg and preferably include some fibre-rich pulses, wholegrains, fruit and nuts.

Be wary of claims of special fat burning, quick-fix, powers. If a diet sounds too good to be true – then it is!