Do ‘Negative-Calorie’ Foods Exist?

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Do ‘negative-calorie’ foods exist?

Check out this answer from Consensus:

The concept of negative-calorie foods is more myth than reality. Empirical studies have shown that while certain foods like celery can contribute to a negative energy balance, they do not result in a net energy deficit. Both negative-calorie and low-calorie diets can be effective for weight loss, but the former does not offer unique advantages. Additionally, the negative calorie illusion can lead to misconceptions about food choices. Therefore, a balanced diet and regular exercise remain the most reliable strategies for weight loss and health improvement.

The concept of “negative-calorie” foods has intrigued many in the field of nutrition and weight loss. These foods are believed to require more energy for digestion and assimilation than they provide, theoretically leading to a net energy deficit. Common examples often cited include celery, cucumbers, and other high-water, high-fiber, and low-calorie foods. This article aims to explore the scientific validity of negative-calorie foods and their potential impact on weight loss and health.

What Are Negative-Calorie Foods?

Negative-calorie foods are those that purportedly require more energy to digest than the calories they contain. The idea is that the thermic effect of food (TEF), which is the energy expended to digest, absorb, and metabolize nutrients, exceeds the caloric content of the food itself. This concept has been popularized in various diet plans and weight loss strategies.

Empirical Evidence

Study on Celery and Bearded Dragons

One empirical study aimed to test the validity of negative-calorie foods using celery, a commonly cited example, and the bearded dragon (Pogona vitticeps) as the test subject. The study measured the postprandial metabolic rates and energy lost to excretion. The results showed that while a significant portion of the meal’s energy was lost to feces, urate, and specific dynamic action (SDA), there was still a net gain of 24% of the meal’s energy. This study debunks the idea that celery or similar foods are truly negative-calorie but suggests they can contribute to a negative energy balance and weight loss.

Human Studies on Negative-Calorie Diets

Overweight Women

A clinical trial compared the effects of a negative-calorie food (NCF) diet and a low-calorie food (LCF) diet on weight and lipid profiles in overweight women. Both diets resulted in significant weight loss and improvements in lipid profiles. However, the NCF diet did not show superior results compared to the LCF diet, indicating that NCFs are not a healthier choice for weight loss in sedentary overweight females.

Middle-Aged and Older Men

Another study investigated the effects of a negative-calorie diet (NCD) supplemented with exercise compared to a low-calorie diet (LCD) with exercise in overweight and obese middle-aged and older men. Both diets led to significant weight loss and improvements in lipid profiles. The study concluded that both diets were equally effective, challenging the notion that NCDs offer unique benefits.

The Negative Calorie Illusion

A psychological aspect of negative-calorie foods is the “negative calorie illusion,” where people estimate the caloric content of a vice food (e.g., cheeseburger) to be lower when paired with a virtue food (e.g., celery sticks). This illusion can lead to misleading perceptions about the healthiness of certain food combinations. Studies attempting to replicate this finding have shown mixed results, suggesting that the illusion is not a robust effect and may arise from contrast effects and lack of calorie-content knowledge.



Do ‘negative-calorie’ foods exist?

Louise Dunford has answered Unlikely

An expert from De Montfort University (DMU) in Nutrition, Obesity, Dermatology

Diets are everywhere, but could eating “negative calorie” foods, such as celery and grapefruit, help to boost weight loss?

A calorie is a unit of energy, usually expressed as kilocalories (kcal) for the energy content in food. The theory behind negative calorie foods is that some foods have lower calorie (energy) content than the amount of energy it takes to digest and absorb the food into the body. This sounds plausible, in theory. But in reality, even the lowest calorie foods, such as celery, contain more calories than it takes to break down and absorb them in the body.

Our energy needs are made up of three components:

  • The energy needed to maintain a body at rest, which is the energy needed for our body to carry out its basic processes so we can live.
  • The thermic effect of eating, which is the increase in metabolic rate after eating, while food is digested and absorbed.
  • Additional energy needed for activity and exercise.

Of these, the thermic effect uses the fewest calories – about 10% of the energy we take in. In other words, about a tenth of the calories we eat are used to process our food – this includes chewing our food, moving it through the digestive system, absorbing nutrients and storing excess energy.

Foods such as celery, grapefruit, broccoli, tomatoes and cucumber have all been touted as negative calorie foods, but there is no scientific evidence to support this idea. Although they are very low calorie foods, with seven to 30 kcal per 100g, it still takes less energy than this to process them. This is because they contain large amounts of water and fibre, which have a very low energy cost.

Replace, don’t add

These foods are very useful for people who are trying to lose weight, as they contain a low number of calories. By replacing the food in your diet with some of these – for example, replacing a side portion of chips with a side salad – it is possible to lower your calorie intake considerably. As an extra boost, they are full of nutrients, such as vitamins and minerals, and also contain a lot of fibre, which also has many benefits for your health.

Healthier options should replace higher calorie foods in a meal, not just be added to it. 

It’s important to replace higher calorie items on a plate rather than add these fruit and vegetables to meals, as by simply adding healthy items you increase the overall calorie content. For example, a cheeseburger plus a salad contains more calories than a cheeseburger alone.

In order to lose weight, people need to use up more energy than the energy (calories) they eat and drink, but this is difficult. Research has shown that people tend to underestimate the calorie content of the food they consume, and they underestimate it by more if they are obese rather than normal weight.

Researchers have also shown that when people visit fast food chains with a healthier image, they underestimate the calorie content of their meals, compared with the same meals at a restaurant with a less healthy image and may end up consuming more calories overall.

Another difficulty is keeping weight off in the long run. Many studies have shown the short-term benefits of diets to help with weight loss, but over 80% of people put the weight back on again over time. In many modern societies, there is easy access to cheap high-calorie foods, so it is difficult to resist high fat/sugar options on a permanent basis.

Unfortunately, negative calorie foods are a myth, and there is no easy way to lose weight and keep it off in the long run. Changing your food and drink options for healthier ones on a permanent basis is more likely to lead to sustained long-term weight loss than short-term dieting alone.

I have adapted this answer from my original article in The Conversation


Do ‘negative-calorie’ foods exist?

Tim Crowe has answered Extremely Unlikely

An expert from Thinking Nutrition in Nutrition

A favourite myth is the concept of ‘negative calorie foods’ such as celery, which burn up more energy than you consume. If only it was as simple as eating your way to thinness. But there is no such thing as a negative calorie food. Even the humble stick of celery, while being about 95 percent water, still contains a small number of kilojoules from carbohydrate (65 kJ to be exact). There is though an energy cost to your body in digesting food, called the thermic effect of food, but that equates to about 10 percent of the energy in the food. So even celery adds some kilojoules to your diet. And while it’s a small number, it’s definitely not a negative number. How foods like celery, lettuce and broccoli can help you lose weight is if your mouth is full of celery, then there’s no room to fit in burgers and fries.


Do ‘negative-calorie’ foods exist?

Cornelie Nienaber-Rousseau has answered Uncertain

An expert from North-West University in Nutrition

The so-called negative-calorie or negative-energy food or beverage is a food or drink for which the energy required to process (digest, absorb, transport, metabolise and store ingested nutrients) it exceeds the energy contained therein. The energy required for the processing of food is called the thermic effect of food or the specific dynamic effect or specific dynamic energy.

Water contains no energy and when drinking water outside body temperature ranges will expend some energy to maintain the body’s internal temperature i.e. the so called water-induced thermogenesis effect. Because one kcalorie heat energy is needed to raise the temperature of 1 kg of water with 1°C, raising 250 g (a normal glass) of water at 3 to 4°C (temperature in a fridge) by 33.5 °C to equal body temperature will take 33.5 kcalories/1000g x 250 g of water, which equals 8.040 kcalories (x by 4.2 to converted to kJ = 33.8). Boschmann and co-workers (2003) reported that drinking 500 ml of water increased the metabolic rate by 30% – the highest reported to date with most studies not showing any (see summary of literature in Brown et al. (2006) Table 1) increase and two reporting a 2.7% (Kamatsu et al., 2003) and 2% increase (Brundin & Wahren, 1993), respectively. Brown and colleagues (2006) in an effort to replicate the work of Boschmann and co-researchers, studied whether water has a thermogenic effect and whether this effect is influenced by osmolality or by water temperature. They found that drinking either distilled or saline water did not result in energy expenditure, but that sugar (sucrose) water resulted in energy use. Brown and co-workers reported a mere 4.5% increase in energy use over 60 min after participants consumed 7.5 ml/kg body weight of water at 3°C. Even though water-induced thermogenesis might not result in increased energy expenditure, substituting high energy beverages (empty calorie beverages such as sodas) with water will most certainly result in weight loss (Tate and co-workers, 1993) . One of the South African food based dietary guidelines is to drink plenty of clean safe water (van Graan et al., 2013) – keeping in mind that too much could lead to water intoxication.

Chewing gum (not bubble gum – the latter usually contains added starches and is sweetened with sugar) could be considered to be a negative-energy food, but keep in mind that the thermic effect of food is reduced when foods bypasses the mouth. Mastication merely burns 11 kcal (46.2 kJ) per hour (Levine & Pavlidis, 1999) and can therefore hardly be considered as being real exercise. Because one stick of gum contains around 10 kcal (42.0 kJ), it will require being chewed for one or more hours to burn the energy the gum provides. Swoboda and Temple (2013) hypothesised that chewing gum before eating might reduce motivation to eat, hunger and energy intake. However, they did not find promising results in this regard. They observed that chewing mint gum reduced intake of fruit, possibly reducing diet quality. Chewing gum before each eating occasion reduced meal frequency, but increased meal size. Xu and co-researchers (2015) asked non-obese men to chew sugarless gum for 30 minutes following a meal in order to study neural mechanisms regulating the secretion of glucagon-like peptide-1 (GLP-1). Gum chewers reported feeling fuller than non-gum-chewers as early as 5 minutes after beginning to chew even when no differences in the blood concentration of glucose, insulin and glucose-dependent insulinotropic peptide or hunger were observed. Ikeda and co-researchers (2018) observed that chewing tasteless gum reduced subjective appetite and may affect reward circuits to help prevent impulsive eating. Shikany and co-workers (2001) used a 8-week randomized controlled trial (the golden standard study design to test cause and effect) to evaluate the effects of chewing gum for a minimum of 90 min/day on body weight in 201 overweight and obese adults together with receiving good nutritional advice. Theirs are one of few experimental studies and they concluded that chewing gum on a regular schedule did not facilitate weight loss above only receiving nutritional information. The sugar alcohols used to sweeten chewing gum might be beneficial, because xylitol seems to reduce the occurrence of dental caries (as summarised in a systematic review and meta-analysis by Janakiram et al. published in 2017). A word of caution is necessary here, as case studies indicated that chronic diarrhoea and severe weight loss could be caused by the sugar alcohol sorbitol in chewing gum (Bauditz et al., 2008). Even though mastication might not burn substantial amounts of energy and that chewing gum might not lead to significant weight loss, there are a summary of 17 trials showing that increasing chews per bite of actual food could be used to control cravings by inducing feeling satiated for longer (Miquel-Kergoat et al., 2015).

Diabetics and those who have to control food intake will be acquainted with so-called ‘free foods’ or nutritionally trivial food some of which could also be considered to be energy-negative. These foods are defined as “any food or drink that contains less than 20 calories (84 kJ) or less than 5 g of carbohydrate per serving” (Mahan & Escott-Stump, 2008). These include celery, berries, grapefruit, carrots, tomatoes, cucumbers, watermelon, apples, zucchini (baby marrow), broccoli, cabbage and lettuce among others. When Buddemeyer et al. (2020) tested the validity of celery as a negative energy foods (to take its “free food” categorisation further to being a negative-energy food) in lizards. They concluded that celery contains more energy than needed for digesting and assimilation and do not result in an energy deficit, but overall the inclusion of low energy dense foods do contribute to a negative energy budget and thus weight loss in those who are physically active. Reducing energy intake by including low energy containing foods are key to keep the dieter from feeling hungry, while keeping energy intake low. Foods considered to be of negative-energy or free has such low energy content that dieters could consume them when feeling peckish or thirsty without risking weight gain. Note that one should not confuse these foods with empty calorie foods which are on the opposite side of the spectrum providing huge amounts of energy while lacking in micro-nutrients (vitamins and minerals). Diets based on so-called negative-calorie food or to use the more acceptable term ‘free foods’ do not work because they cause an energy deficit, but rather because these foods satisfy hunger by filling the stomach with food that is not energy dense and coupled with exercise can lead to burning more fuel than was ingested to create an overall energy deficit. However, a word of caution is needed. Studies indicate that people would underestimate the energy content of a food/meal when a healthy food such as free food is present – this phenomenon coined by Chernev as the ‘negative calorie illusion” (Chernev, 2010; Forwood et al., 2013). Paradoxically, Chernev (2010) observed that those who were more concerned with their body weight and management thereof (the ‘weight-conscious’) were more prone to this bias. Dietitians should educate their patients on how to estimate a food’s energy value more accurately and not to be deceived by the presence a healthy food that could lead to a perceptual bias and ultimately weight gain. While the theory behind the negative-calorie foods seems solid at least for cold water and chewing gum but will not result in noteworthy weight loss, the study by Buddemeyer and co-workers (2020) albeit in reptiles questions their very existence. Further research is needed to confirm or refute negative-energy food’s or drink’s scientific validity.

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