Very Low Calorie Diets (VLCDs)

A well-known VLCD is The Cambridge Diet. Lighter Life is another VLCD.

The VLCD is, as its name suggests, very low in Calories and is aimed at morbidly obese people i.e. people who have a Body Mass Index (BMI) of over 40. Such people are at a very high risk of dropping dead of a heart attack and they are also at a high risk of complications caused by high blood pressure, high blood glucose, high blood triglycerides, high blood cholesterol, high blood LDL-c, low blood HDL-c and high blood uric acid. In addition, morbidly obese people have breathing problems e.g. sleep apnoea and they are also at a high risk of dying while under anaesthetic if they need to be operated on. Such people need to lose weight rapidly. However, people who are overweight (BMI 25-29.9) or obese (BMI 30-39.9) or who are just unhappy with their bodies should not embark on a VLCD as the risks outweigh the benefits.

1) VLCDs result in rapid weight loss. You may think that this is a good thing, but rapid weight loss brings with it problems.

a) Excessive loss of muscle. This is more of a problem for women who, because they have naturally-low testosterone levels, have great difficulty regaining any lost muscle.

b) High risk of developing Gallstones. Rapid weight loss results in an increase in the concentration of cholesterol in bile. This increases the risk factor for gallstones, something that women have a higher risk factor for than men. There's an acronym FFFF for people who are at a high risk of developing gallstones. It stands for Female, Forty, Fat, Fair. What makes the situation even worse is that VLCDs are very low in fat. The gallbladder is a muscular bag which stores bile. When dietary fat is eaten, this stimulates the secretion of cholecystokinin, which then stimulates contraction of the gallbladder muscle, which expels bile from inside the gallbladder into the duodenum. The lower the fat content of a meal, the less the gallbladder contracts and gallbladder stasis can result with only 2g of fat per meal. See The role of gallbladder emptying in gallstone formation during diet-induced rapid weight loss. The problem with this study is that the two groups of subjects were not eating the same number of calories. See Gallbladder motility and gallstone formation in obese patients following very low calorie diets. Use it (fat) to lose it (well) and Similarity in gallstone formation from 900 kcal/day diets containing 16 g vs 30 g of daily fat: evidence that fat restriction is not the main culprit of cholelithiasis during rapid weight reduction.
In these studies, both groups were on the same calorie intake. In the second study, 17% of the low-fat group developed gallstones whereas only 11.2% of the higher-fat group developed gallstones.

The other problem with a very low fat intake is EFA deficiency. Essential Fatty Acids are called that for a reason....they are essential for us to live. Dry skin & hair are common on VLCDs. The small amount of fat that there is in a VLCD almost certainly contains mostly omega-6 polyunsaturates. A lack of omega-3 EFAs can adversely affect mental function. Depression is common on VLCDs. See Omega-3 fatty acids and major depression: A primer for the mental health professional. Another problem with very low fat intakes is a lack of fat-soluble vitamins, particularly Vitamins D3 and K. See Vitamin D and Vitamin K.

2) VLCDs contain excessive amounts of sugars. This has two problems.

a) Unstable blood glucose levels. See Blood Glucose, Insulin & Diabetes. You don't notice peaks in blood glucose. However, dips cause severe hunger pangs and, in some people, neurosis. See Hypoglycemia & Neurosis.

b) Carbohydrates fill glycogen stores. As glycogen stores become filled, fat-burning decreases. When glycogen stores become full, fat-burning falls to zero. Fat-burning increases again as glycogen stores deplete between meals - but you feel hungry.

Sedentary people's bodies don't burn much carbohydrate. See Everyone is Different. At rest, on average a fasted person derives ~65% of energy from fats and ~35% from carbohydrate, although there are extremes of 93% fat-burning to 20% fat-burning. Even if someone who has full glycogen stores derives 100% of their energy at rest from carbohydrate, as they are only burning ~1kcal/minute at rest, their body is only burning 0.25g of carbohydrate/minute. So why feed someone carbohydrate when their body doesn't need it?

c) People with excess belly fat almost certainly have The Metabolic Syndrome. This causes various problems including high serum triglycerides (TGs). Eating carbohydrate that isn't burned and can't be stored raises TGs. I know about this as I have blood test results which showed TGs increasing with increasing carbohydrate intake. High TGs are bad news for your arteries. See Cholesterol And Coronary Heart Disease.

3) VLCDs don't contain enough protein. Protein supplies Amino Acids (AAs) to the body. These are used to preserve muscle mass. AAs can also be used to generate blood glucose in the liver by a process called Gluconeogenesis (GNG), which makes the consumption of carbohydrates redundant for most sedentary people.

4) VLCDs don't contain enough fibre/fiber. Constipation is common on VLCDs.

In my next Blog post, I will discuss a Rapid Fat Loss alternative to the VLCD that overcomes all of the above problems and is therefore much safer and more pleasant to be on. See The Protein-Sparing Modified Fast (PSMF)

For a discussion of VLCDs, see What do you think of Very Low Energy Diets?