The diet could reinforce bad eating habits. Bon Appetit/ Shutterstock
The “metabolic confusion” diet is one of the latest fad diets to be blowing up on social media. Like many fad diets, it promises you can lose weight while still eating what you want.
Fans of the diet claim that by switching between very low calorie days and high calorie days, you can lose weight while simultaneously speeding up your metabolism. It may sound promising, but there’s no research to back these claims.
The metabolic confusion diet is similar to intermittent fasting, but without the extremes of energy (calorie) restriction. A person on the diet might, for example, eat only 1,200 calories one day, then eat 2,000 calories the next. Although there hasn’t been any research looking specifically at the metabolic confusion diet, we might compare it with a popular form of intermittent fasting: the 5:2 diet where you eat as usual for five days, then either fast for two days or only eat around 500 calories.
Despite being able to eat as much as you like on “feed days”, people may not feel more hungry and still end up eating less overall – and even less on the feed days than they did before starting intermittent fasting. This supports the idea that intermittent fasting can lead to comparable weight loss as conventional diets, where you restrict calories daily.
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But while these diets may be successful in getting people to eat less, they may actually reinforce bad eating habits and poor diet quality (such as consuming high-energy, highly-processed foods and drinks), as people may think they can “treat” themselves following low-calorie days. Indeed, research has shown people following these diets have a less nutritious diet than those following traditional calorie-controlled diets.
Other studies have shown that people following the 5:2 diet consume more calories before fast days unconsciously – which could very well happen on the metabolic confusion diet, too.
The other reason for the metabolic confusion diet’s popularity is because fans of the diet claim that switching between low- and high-calorie days keeps your metabolism active, causing you to burn more calories as a result. It’s also believed that this “confusion” will stop biological resistance – such as an increase in appetite – to the diet that may derail weight loss or cause you to regain any weight you’ve lost.
But when we lose weight, our body needs fewer calories to survive. These changes to our metabolic rate (the baseline amount of calories our body needs to function daily) can even be seen several years following weight loss. This is thought to be the result of body mechanisms that adjust the metabolic rate downwards through a special process (called adaptive thermogenesis). This process aims to stop energy from being wasted by preserving it in fat tissue and other fuel reserves. Increased appetite is another way the body tries to restore lost body weight.
The other key selling point of the metabolic confusion diet is that it prevents your metabolism from slowing as you lose weight. However, when we look at studies on intermittent fasting, we see the same reduction in resting metabolic rate as traditional calorie-restricted diets do.
The odd study that has suggested intermittent fasting raises your metabolic rate can often be explained by the inclusion of total fasting.
Fasting causes an acute metabolic starvation response, leading the body to burn through more of its reserved fuel for around 24-48 hours after a fast. All short-term emergency fuel management measures to glucose supply to the brain. But even in this case, any temporary increase in metabolism may be barely detectable. Also, some studies have actually shown greater reductions in metabolic rate with intermittent fasting.
The truth is that no matter how you lose weight, your metabolic rate will decrease. Even certain types of exercise, may not necessarily increase metabolism – with studies on endurance training (such as long-distance running) showing that metabolic rate slows in order to use energy more efficiently during exercise. However, the body does burn more calories immediately after exercise to help muscles recover, especially after higher intensity exercise. Regular weight training could potentially lead to a higher metabolic rate.
But if the metabolic confusion diet functions similarly to intermittent fasting, it may have other benefits beyond just weight loss.
Intermittent periods of energy restriction have been shown to improve glucose (blood sugar) and lipid (fat) metabolism. This means the body is better able to deal with carbohydrate and fat from a meal. This makes the body better able to tolerate indulgent foods when we encounter them.
By this token intermittent fasting-type diets can improve your ability to manage fuels in the body – known as metabolic flexibility. Metabolic flexibility means you’re better at burning and storing carbohydrates when you need to, and equally better at managing the storage and release of fat from fat stores. This improves insulin sensitivity, which reduces overall risk from disease, such as cardiovascular disease and diabetes. All of this is independent of weight or weight loss.
Although the metabolic confusion diet may be just another fad diet, it may have benefits other than losing weight given it’s similarity to intermittent fasting. While it can’t “speed up” your metabolism, diets that allow us to have more flexibility in the way we eat are more sustainable and easier to follow in the long run.
About the Author
Adam Collins, Senior Teaching Fellow, Nutrition, University of Surrey