A meal replacement diet is one that replaces your regular meals with low-kilojoule powdered shakes and snack bars to lessen your overall energy intake, which can prove to be a catalyst in your weight-loss journey.

If you can take consuming shakes and bars for breakfast, and even in some cases, both lunch and dinner, then evidence points to meal replacements being a worthy weight-loss tool for the short term. But they’re certainly not a permanent fix, and before you begin with any weight loss diet, you should consult your GP. And before you go start a meal replacement diet, perhaps it would be prudent for you to read up and learn a few things about it.

How do they work?

Meal replacements are kilojoule-controlled goods that are geared to facilitate quick weight loss and conserve lean body mass. The formulas that are used are mainly protein-based, have a few carbohydrates and are packed with vitamins and minerals.

“What meal replacements try to do is cover the body’s protein requirements in as few kilojoules as possible,” said Clare Collins, a professor of nutrition and dietetics at the University of Newcastle.

However, not all shakes and bars are supplemented the right way as some contain high sugar levels which aren’t advisable for those that are trying to shed weight.

To make sure that what you’re purchasing have the essential vitamins and minerals, look for products that have the label “formulated meal replacement.” These are governed by food standards established by Food Standards Australia and New Zealand.

Very low energy diets

Like any regimen that emboldens an energy deficit, the concept of meal replacements is to consume fewer kilojoules (or calories) than you utilise in your daily activities.

To do this, meal replacements were made designed to take the place of all daily meals in what is called a “very low energy diet.”

To make sense of that, the average person basically needs roughly 8,700 kilojoules per day to maintain their current body weight. On a very low energy diet, you’re restricted to around a quarter of that: which is 1,800 to 2,500 kilojoules per day.

“If you stick to that, you’re going to lose weight fast, provided it doesn’t make you feel so bad that you are a lot less active than you normally would be,” Collins remarked.

When your total kilojoule intake is held in check, the fuel stores in your muscles which are called glycogen start to run on fumes. Once this happens, your body is left with no other course of action but to turn to its fat stores and burn fat for fuel. This process is known as ketosis.

Very low energy diets are more likely to be suggested to adults with obesity who need to lose a large amount of weight in a short period of time. This is often done for health reasons, such as ahead of bariatric surgery, or to bolster specific medical issues.

Oftentimes, this involves replacing all meals with meal replacements except for the addition of a small bowl of salad or vegetables every day, which is done to boost fibre and other nutrients, and a small amount of oil to keep your gall bladder working, for six weeks.

This type of fasting needs the supervision of a trained professional with monitoring being conducted by a GP, a dietician or a specialized nurse.

Partial meal replacements

Meal replacements can also be done on a partial basis, which means replacing one or two meals per day.

As mentioned above, this is also best for just in the short term, and needs to be carefully supervised as part of a long-term approach to a healthy diet, according to Collins.

“The more days you have a restricted type of eating pattern or a severe kilojoule restriction, the more important it is that on the other days, your nutrient intake is maximised by following a very healthy eating pattern.”

“You need to get enough fibre, folate, B vitamins, iodine, iron, zinc and other essential nutrients, so that you don’t end up with some sort of nutrient deficiency because your diet is so restricted,” said Collins.

Collins explained that because of the potential for nutrient deficiencies, among other danger factors such as gall bladder and liver inflammation, any diet that includes meal replacements need utmost guidance from a health professional.

“Before you jump in and try meal replacements [on a regular basis], it’s a really good idea to go and see your GP for a health check. You probably need to have a blood test, check your liver function, get a referral to a dietician, and talk to your GP about monitoring your health while you are on a weight loss diet,” cited Collins.

The National Health and Medical Research Council also proposes that anyone who goes through the meal replacement diet as a weight-loss strategy should ask for help from a healthcare professional to make sure they manage the diet safely and without adverse health effects.