The idea that humans can get all the nutrition they need in a pill or a drink has been the stuff of science fiction for decades. Today, life is imitating art, with many companies claiming to produce powders which, when mixed with milk, water or juice, can provide all the nutrients we need in a single efficient, calorie-controlled portion.
Such drinks are often used as diet aids and at the popular end of the market - where drinks like Slim Fast (and its various copycats) live - the meal in a glass means that hopeful slimmers don't have to spend hours thinking about food, weighing food and balancing food groups in order to lose weight.
For very obese individuals, this type of calorie-controlled regime has been proven in medical studies (albeit, more often than not, funded by Slim Fast) to be moderately successful - at least in the short term.
In one Finnish study, for example, 100 participants were given either conventional foods or a regime where meal replacements (Slim Fast shakes, bars and soups) were substituted for two of the three main meals. In the first three months of the trial, the meal replacement group lost, on average, 7.8 per cent of their starting body weight, compared with 1.5 per cent in the food group (Am J Clin Nutr, 1999; 69: 198-204).
Further follow-up at four years showed that those who continued replacing one meal daily with a meal replacement maintained their weight loss (Obes Res, 2000; 8: 399-402).
Another study, which substituted three meals a day with calorie-controlled shakes (supplemented with fruits and vegetables) over three months, resulted in similar weight loss compared with a diet where women had a free choice of foods up to 1200 calories per day. However, in the following nine months, only those who continued to use the meal replacement for one meal per day maintained their initial weight loss (J Am Diet Assoc, 2001; 101: 345-7).
Nevertheless, meals in a glass have been criticised because they do not contribute to improved eating habits (J Am Diet Assoc, 1991; 91: 1243-5; Int J Obes, 1999; 23: 553- 5; J Consult Clin Psych, 1999; 67: 177-85; Exp Clin End, 1998; 10: 22-6). Studies into their effectiveness may also be misleading because, even though weight reduction is generally beneficial, the simple fact of weight loss is not the best indicator of health (Am J Epidemiol, 1996; 143: 228- 39; Nutr Rev, 1987; 45: 225-31).
Can't get no satisfaction?
Intriguing evidence also suggests that the body does not recognise calories from liquids as effectively as it does calories from solid foods. In one study, otherwise free-eating participants were asked to consume 450 calories' worth of jelly beans every day for four weeks and then 450 calories' worth of soda every day for another week, and to keep a record of what they ate each day.
On the days the participants ate the candies, they compensated by eating roughly 450 fewer calories' worth of other foods - so no more calories than usual were ingested. But on the days they drank the sodas, the subjects didn't compensate and, in fact, ate roughly 450 calories more than usual. The researchers concluded that liquid calories don't trip our satiety mechanisms as effectively as do solids (Int J Obes Relat Metab Disord, 2000; 24: 794-800).
Another study looked at the same problem from two different angles. First, test subjects were given meals identical in caloric content, weight, volume, composition and temperature, but differed in that one was liquid and the other solid. In the second part of the study, the test meals were composed of a liquid item and a solid item. Both test meals were identical except that, in one meal, the majority of calories came from liquid while, in the other, the majority were from solid food. Results of the first part of the experiment showed that the food intake in the 24 hours after the liquid meal was higher than after the solid meal. Similarly, results of the second part showed that when the majority of calories in the meal was consumed in liquid form, the subsequent calorie intake was higher (Appetite, 1991; 16: 17-24).
One study found that men who consumed a calorie-containing beverage with their meals wound up consuming more calories than if they drank a calorie-free beverage (Physiol Behav, 1990; 58: 19-26).
Judging any type of food is often a subjective exercise. While we allocated points for the taste and texture of the shakes, we also looked for objective markers of nutritional quality. Each product was assessed according to its carbohydrate and protein content. We took points off for excessive sugar content, and also for megadoses of protein, which can be just as unhealthy (see box on page 3 ). We looked at vitamin and mineral content as well as calories per serving and fibre content. We also looked for extra and dubious ingredients such as artificial sweeteners. Finally, we looked at price, including a pint of milk (40 p) where appropriate. As each of these products has a different serving size, ranging from 220-330 mL, to make a fair comparison, we broke the price down into both per serving and per 100 mL of each product.
For an overall comparison, we used guidelines from the London-based Institute for Optimum Nutrition, which suggest that a well-balanced diet should be made up of approximately 15 per cent protein, 70 per cent carbohydrate and 15 per cent fat, with a daily fibre intake of around 35-45 g.
On this basis, none of the products tested came even close to being well-balanced, and some were little different from standard chocolate milk drinks (see box above for comparisons). Although users are supposed to include at least one 'well-balanced' meal daily on a meal-replacement regime, with most of these products, this would still not necessarily guarantee an overall balanced diet. In those drinks that have a greater carbohydrate-to-protein ratio, the carbohydrates are made up mainly of sugars, which effectively negate any potential benefit. We would also have liked to have seen much more advice with each of these products about drinking water - especially necessary with the higher-protein shakes and for drinks containing fibre.
Price: lb1.49 for 330 mL
This premixed meal replacement is one of many made by EAS (Experimental and Applied Sciences), one of the more popular manufacturers in the US. Previously available only through branches of the American healthfood chain GNC, these products are finding their way into independent healthfood shops, and can now even be found in larger branches of some supermarket chains such as Sainsbury's.
EAS makes a number of products for serious bodybuilders, including the popular Myoplex - a high-protein, low-carbohydrate nutrition shake.
AdvantEdge, however, is aimed squarely at the Slim Fast market, and there is little between the two products in terms of their sugar content, caloric values, and levels of vitamins and minerals they offer. The vanilla and chocolate flavours are acceptable and have a reasonably creamy texture, but it's best served cold. However, AdvantEdge contains chromium, which can enhance insulin sensitivity, so we were surprised to find no warning to diabetics, who should avoid products with this mineral.
At lb1.49 per serving, or 45 p per 100 mL, you are probably paying more for the convenience factor of a premixed drink and the association with a known sport-nutrition company.
Price: lb34.99 for 20 85-g sachets (20 servings)
A serious meal replacement for gym addicts, this is relatively high in calories (320 per serving) compared with its competitors and contains a massive 52.7 g of protein per serving when mixed as directed with water. Replacing two meals a day would give you a decent amount of calories, but also almost five times the adult recommended daily intake of protein. Unusually, this product derives its protein from whey, which makes for a creamier-tasting mixture. But its high protein content means that it is only suitable for those who are involved in regular, strenuous body-building, whose protein requirements are much higher than average. It also contains the artificial sweetener acesulfame K and sugar-free sweetener xylitol, both of which can cause stomach upsets.
Max-Meal costs lb1.75 per serving, or approximately 50 p per 100 mL.
Distributor: Sun Nutritional
Price: lb6.49 for a 420-g can (12 servings)
The best known of all these meal replacements is a soya-based drink. It contains no artificial sweeteners, but plenty of sugar, which may be part of its appeal. To be palatable, Slim Fast needs to be mixed in a blender with very cold milk and preferably ice - which seems to help thicken it. Mixed in this way, it's like drinking a milkshake for lunch, and this guilty pleasure may be one reason why Slim Fast is a market leader.
Slim Fast comes in chocolate, vanilla, strawberry and banana flavours, and can be put in a blender with fruit to boost both the nutritional quality and taste. A single serving of Slim Fast has more fibre than all the other drinks combined. Some of this fibre content is from inulin (an important water-soluble fibre obtained from Jerusalem artichokes).
The cost of a Slim Fast drink is around 70 p per serving, or 32 p per 100 mL.
Distributor: Nature's Plus
Price: lb16.95 for 476 g (14 servings)
Manufacturer Nature's Plus claims on the label that one of the ingredients is love. This soya-based shake also contains spirulina, a type of algae, as well as added oat bran and apple pectin. Despite this, it is very low in fibre, so long-term use may mean that dieters won't get the fibre they need. Soya protein can also be difficult to digest, which may be why this product includes papaya and the digestive enzyme bromelain. However, it also contains chromium, so diabetics should beware.
Spiru-Tein comes in vanilla and chocolate flavours, and can be mixed with water, milk or juice (vanilla is probably more appropriate for the latter). For best results, the liquid should be very cold and, although it is supposed to mix instantly, we found that using a blender gave better results.
The cost when mixed with milk worked out at lb1.37 per serving, or 62 p per 100 mL.
Price: lb22.99 for 708 g (19 servings)
Diet Fuel contains no fat, no fibre and no sugar. Mixed as recommended with 8 oz of water, this drink tasted much like you'd expect 120 calories to taste - thin and uninteresting. In a blender with ice, the chocolate had more appeal; the vanilla mixed with fruit stood up better too. Yet again, though, it contains chromium picolinate, which diabetics should avoid except when taken under medical supervision. Also, it uses aspartame, which can cause uncomfortable symptoms such as heart palpitations and headaches.
Following a regime that replaces two or three meals daily with this product would mean you are taking in less than 1000 calories daily - a dangerously low level.
Ironically, given how little is in it, this was the among the more expensive brands we surveyed. Dining on Diet Fuel will cost you lb1.21 per serving or 55 p per 100 mL.
Source of Life
Distributor: Nature's Plus
Price: lb18.35 for 507 g (13 servings)
An 'energy shake' based on (non-GMO) soya protein, the ingredients in this mix differ significantly from the others in this review. Source of Life is more of a supplement than a meal in a glass, and uses concentrated whole foods to provide a reasonable range of vitamins and minerals. It includes fruit and vegetable concentrates, bioflavonoids, digestive enzymes, good fats, carotenoids, bee pollen, ginseng, Astragalus, ligstrum berry, schisandra, barley, Echinacea, Irish moss, thyme and spirulina.
This may be most useful for convalescents or children who won't eat. The green colour may put some people off and, even with vanilla flavouring, a slight aftertaste of spirulina lingers. Mixed with milk, it costs lb1.73 per serving, or 78 p per 100 mL - the most expensive drink we tested.
Fast food is here to stay and the market for liquid meal replacements is growing each year. Nevertheless, if this investigation is anything to go by, we are still a long way from the science fiction ideal of a truly well-balanced and nutritious meal in a glass.
Product Calories Protein Carbohydrate (sugars) Fats (saturates) Fibre
AdvantEdge 200 15.0 27.0 (23) 4.6 (0) 1.1
Diet Fuel 120 20.0 9.0 (0) 0 (0) 0
Max-Meal 320 52.7 10.4 (2.6) 8.0 (5.7) 1.87
Slim Fast* 213 13.8 32.0 (27.6) 3.5 (0.8) 6.0
Source of Life 196 21.0 28.0 (21) 0 (0) 1.0
Spiru-Tein 176 22.0 22.0 (18) 0 (0) 1.0
And just for the record . . .
Ovaltine** 185 8.4 29.6 (21.7) 3.7 (2.3) 0.6
All figures except for calories denote grams per serving; *Chocolate Royale flavour;
**Original formulation, mixed with 200 mg skimmed milk (28 pence per serving)
It pays to look at the label with a critical eye when choosing meal replacements. Important information includes:
Many meal replacements claim to give you energy. Think carefully about this claim as energy is just another word for calories. The energy-boosting carbohydrates in most meal replacements are often just sugar. In fact, in some of them, sugar is the main ingredient, though often dressed up in a selection of other names such as fructose, glucose, dextrose, maltose, corn syrup, rice syrup and barley syrup. Sugar contains no nutrients and the energy you get from it is short-lasting and often followed by more pronounced feelings of fatigue and a loss of energy.
Even less satisfactorily, those that don't contain sugar use artificial sweeteners, such as the excitotoxin aspartame and acesulfame K. These neurotoxic compounds have been associated with a variety of problems, ranging from headache, skin rash and digestive disorders to brain tumours (J Neuropathol Exp Neurol, 1996; 55: 1115-23). Sugar-free sweeteners such as xylitol, associated with stomach upsets, are also common ingredients.
Protein is hugely hyped as a power nutrient. In reality, the body needs protein, carbohydrates and fat to fuel it properly. Professional body-builders need in excess of 300 g of protein daily. The rest of us only need around 35 g of protein daily. In fact, most of us eat in excess of this, with the average diet containing two to three times what we need. In general, high protein intake over the long term is associated with deteriorating kidney function and even osteoporosis.
Consider also the sources of protein in meal replacements. These days, it is usually soya (in fact, all but one of the sampled drinks was soya-based). Drinking high-protein shakes based on soya several times a day over the long term can potentially result in a body that is profoundly biochemically disrupted. Problems with excessive consumption of non-fermented soya like this are numerous. The high levels of phytic acid in soya reduce the body's absorption of calcium, magnesium, manganese, molybdenum, copper, iron and zinc while increasing the requirement for vitamins E, K, D and B12.
Soya phytoestrogens disrupt endocrine function and are potent antithyroid agents that can lead to hypothyroidism. The processing of soya protein at high temperatures can reduce its nutritive value, and results in toxic lysinoalanine and highly carcinogenic nitrosamines. Soya foods also contain high levels of aluminium, which is toxic to the nervous system and kidneys (see PROOF! vol 4 no 4, pages 2-6). Consumers should remember that soya is often the base for such products not because it is particularly good protein, but because it is cheap.
The other usual source of protein is whey - a dairy-based source of amino acids. While athletes sometimes take extra whey protein supplements, there has not been any evidence that doing so increases athletic performance. People who are allergic to dairy products could react to whey as could those who are lactose-intolerant.
* Other ingredients
These include vitamins and minerals, but also phytochemicals that you have to scrutinise the label carefully to find. Most often, these are digestive aids such as papain and bromelain. But more sophisticated mixes can contain herbal extracts such as ginseng, hydroxycitric acid (a.k.a. CitriMax or Garcinia cambogia), Echinacea, borage oil, garlic, Astragalus, Gingko biloba and even St John's wort. In the world of serious body-building, controversy reigns regarding the addition of herbal anabolic steroid precursors (even if they are not always listed on the label). In the average meal replacement, it is unlikely that these will be present in enough quantity to boost health, though they will help to boost the price of the product.