DIET TRENDS
POPULAR LIQUID DIETS Liquid diets can be essential for certain medical purposes. However, when liquid diets are used for general weight loss, they can be unbalanced or harmful. This article will focus on the nutritional content and evidence related to five popular liquid diets.
Maeve Hanan UK Registered Dietitian Freelance Maeve is a Consultant Dietitian and Health Writer. She also runs the blog Dietetically Speaking.com, which promotes evidence-based nutrition and fights nutritional nonsense.
REFERENCES Please visit: https://www. nhdmag.com/ references.html
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Liquid diets and meal replacements come in various forms. There are some medical indications for liquid diets, such as before or after certain types of surgery, or the use of exclusive enteral nutrition for inducing remission in Crohn’s disease. However, many liquid diets that are promoted as magic bullet solutions for weight loss, are extreme and can be nutritionally harmful. JUICE DIETS
Juice diets involve only consuming juiced fruit and vegetables for about 3-10 days. These diets are often promoted as ‘detoxes’, ‘cleanses’ or ‘juice fasts’. But, of course, no diet can ‘detoxify’ our body, as this is done by our lungs, gut, skin and kidneys. A popular type of juice diet is called ‘the master cleanse’ or the ‘lemoncayenne pepper diet’. This extreme diet involves consuming mainly lemon juice, cayenne pepper, maple syrup and water for 10 days. Raw juice diets are also popular, some of these involve consuming up to two litres of raw fruit and vegetable juice per day! Because juice diets are very low in calories, they can lead to weight loss, although weight tends to be regained when normal eating is resumed.1 Juice diets also tend to be deficient in calories, protein, fat, iron, calcium, vitamin B12, iodine and selenium. Juice ‘cleanses’ can lead to unpleasant side effects, including: bloating, cramping, diarrhoea, dizziness, low energy levels and erratic blood sugar levels. There are also health risks related to juice fasting, which is especially unsuitable for those who are nutritionally
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vulnerable, such as children, pregnant or breastfeeding women, those who are malnourished, or those who have a history of an eating disorder. A high intake of juice may interact with certain medications (such as warfarin). It can also be harmful to undertake a diet like this for those with diabetes, liver disease, kidney disease and thyroid issues (due to high levels of goitrogens found in plant foods). THE CABBAGE SOUP DIET
This fad diet has re-emerged many times over the years and was very popular in the 1980s. This diet involves consuming mainly (you guessed it) cabbage soup for around a week. Some fruit and vegetables or low-fat milk are also allowed on this diet. No studies have investigated the impact of the cabbage soup diet. However, the impact is likely to be very similar to juice diets, as this is very low in calories and provides little to no protein or fat. Therefore, it is another extreme and unbalanced approach, with the likelihood of gut irritation from the high intake of cabbage. WATER FASTING
This usually involves only consuming water for 24 to 72 hours, although black tea and coffee are also sometimes allowed. Water fasting for 24 hours may have similar health benefits to other types of daily intermittent fasting, such as improving metabolic health and reducing inflammation in the body.2 It has been suggested that this may be related to the ‘thrifty genotype theory’
DIET TRENDS
Liquid diets can be essential for certain medical purposes. However, when liquid diets are used for general weight loss, they can be unbalanced or harmful. Juice diets involve only consuming juiced fruit and vegetables for about 3-10 days. that suggests humans have evolved to thrive during cycles of fasting and feasting.3 Fasting might also have benefits for healthy aging, as short periods of fasting may improve the way our body recycles damaged parts of cells (which is known as ‘autophagy’).4-5 However, we don’t have much evidence about how this impacts health in the long-run and many of the studies have been carried out in animals. Some studies have also highlighted harmful side effects of water fasting, including nausea, low energy levels, headaches, high blood pressure, low sodium levels and even serious cases of dehydration.6 The risk of harm from this diet increases depending on the length of the water fast. Overall, water fasting is likely to be an unnecessarily extreme and risky approach for most people. LOW-CALORIE MEAL REPLACEMENT SHAKES
Meal replacement shakes can be used as the sole source of nutrition, or to replace one or two meals per day. The nutritional content of these shakes varies between different products. Some can be low in fibre and it is safe to say that they can’t provide the range and combination of phytonutrients found in wholefood. Meal replacement shakes also can’t replicate the ‘food matrix effect’,
which is the way that the structure and nutrient content of food interacts with each other. For example, consuming omega-3 supplements, or a product which is fortified with omega-3, isn’t seen to have the same health benefits as, eating oily fish.7 Some meal replacement shakes use certain sugar alcohols (polyols) as a low-calorie sweetener. While not inherently bad, this may cause gut issues or trigger IBS symptoms in some people.8 Very low-calorie diets usually involve consuming meal replacement shakes and soups to provide around 800 to 1200 calories per day for up to 12 weeks. These are associated with significant weight loss up to a year after the diet has taken place (although some weight tends to be regained).9 These diets, however, may have useful applications in Type 2 diabetes. For example, the DiRECT trial investigated whether following a very low-calorie diet could put people with Type 2 diabetes into remission.10 This involved consuming only 850 calories per day, in the form of four meal replacement shakes or soups, for three to five months, followed by food reintroduction and ongoing healthy lifestyle support. By the end of the trial, almost 50% of participants had gone into remission and the success rate rose to 86% for
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DIET TRENDS those who lost more than 15kg of weight. This is a promising new area, but it is important to remember that this diet is very restrictive, so it wouldn’t be appropriate for many people and a lot of support is needed to follow the diet in a safe way. A very low intake of calories may slow down metabolic rate due to processes like adaptive thermogenesis and relative energy deficiency (which is often referred to as ‘starvation mode’).11-12 A slightly less extreme approach is replacing one to two meals per day with a meal replacement shake or soup. This has been found to promote weight loss and lead to improvements in blood pressure, cholesterol, blood glucose and insulin levels, when compared with a traditional caloriereduced diet.13 Some people find meal replacement shakes to be a convenient way to reduce their calorie intake. However, they can also be expensive, especially when used over a long period of time. They also do not replicate all of the goodness found in wholefood, and are not advisable for those who struggle with disordered eating. NEW GENERATION MEAL REPLACEMENT SHAKES
In the last five years a new type of meal replacement shake has emerged aimed at busy people who want a nutritionally complete meal in the form of a shake. So, the focus isn’t on weight loss, but convenience and sustainability. Examples of these include Huel and Soylent. These shakes tend to have a good nutritional profile and are suitable for many dietary needs. For example, they are free of common food allergens and are suitable for vegans and
vegetarians. However, as mentioned above, these are unlikely to match the nutritional benefits of a diverse wholefood diet. There is also little to no evidence about the health impact of these specific products. Although one randomised controlled trial from 2016 reported a favourable impact of Soylent on the balance of gut bacteria in 14 participants.14-15 For more information about Huel, go to Alice Fletcher's article in issue 137 (Aug/Sep 2018, www.nhdmag.com/nhd-articles/archive.html).16 CONCLUSION
Faddy liquid diets like juice diets and the cabbage soup diet are not nutritionally balanced and are likely to cause gut issues. There may be some benefits to a 24-hour water fast for some people, but this is a new area of research and there can be serious side effects to water fasting. Low-calorie meal replacements shakes and soups may be useful for some people who are trying to lose weight, and more research is emerging related to their use as part of very low-calorie diets to promote diabetes remission. However, close support and monitoring is needed with this. The new generation of meal replacement shakes (which don’t focus on weight loss) are nutritionally balanced convenient options. However, using meal replacements of any kind is unlikely to match the food matrix effect of wholefood. Furthermore, getting into the habit of drinking meals rather than eating food may encourage an unhealthy relationship with food for some people, especially those with a history of disordered eating.
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Click here to read the Dec/Jan issue Articles include: • Weaning preterm babies
• Nasogastric tube feeding • Fussy eating in toddlers • Constipation and treatment • Popular liquid diets
• Plant-based diets • Care caterers in social care • Follow-on formula new regulations