Why Diets Fail: What the Science Suggests

Dieting has become the norm, but so has diet failure. Dieting usually means restrictive eating in some way, often with a focus on a reduced calorie intake. Diets fail when an individual stops following a specific diet, potentially leading to unwanted weight gain or other health consequences. Studies worldwide have shown that North America has the highest percentage of people attempting to lose weight, and weight loss attempts increase with the prevalence of overweight and obesity. (11) Between 2015 and 2018, 17% of adults 20 years and older in the United States reported following a specific type of diet, the most common being a weight loss or low-calorie diet. (14) Other popular diets include diabetic diets, low-carbohydrate diets, and low-fat or low-cholesterol diets. According to information collected from the 2020 U.S Census data and Simmons National Consumer Survey, 184.83 million Americans were more conscious of their diet. (13) Numerous people start each year by making resolutions to stick to a diet or go to the gym long enough to shed those extra pounds. Yet the diet failure rate is still high and the number of people who are overweight or obese has skyrocketed! Of the 1.9 billion adults who were overweight in 2016, 650 million were obese, (9) and each year, at least 2.8 million people die from the health consequences of being overweight or obese. (9)

New Year’s resolutions often include diet and exercise goals to attempt to lose weight again.

Many studies propose that there is more to weight loss than the removal of certain foods or kinds of food. Continue reading to find out why diets fail and what you can do to improve successful long term weight loss.

Why diets fail

Although there have been many definitions of successful and unsuccessful long-term weight loss over the years, many studies define successful weight loss as intentional weight loss of at least 10% of body weight kept off for at least one year. (17) Therefore, diet failure could be defined as the inability to maintain intentional weight loss of at least 10% of initial body weight for longer than one year. However, some researchers believe that maintaining weight loss of 5% of body weight for a year or more should at least be considered moderate success due to the associated positive metabolic improvements. (12) The reasons for the success or failure of a diet are complex and highly individual. Intrinsic and extrinsic motives, such as desire to improve health or to decrease social stigmatization, have profound effects on the success of a diet. (4)(12)(17) But there are many reasons why 95% of diets fail. (12) According to research, 80% of those who successfully lose weight experience weight regain after one year, 85% regain after two years, and 95% of people regain their weight after three years. Interestingly, the majority of people who regain weight after dieting, gain more weight than previously lost. (12) Our bodies have many natural and automatic processes that make it difficult to follow a restrictive diet. We are surrounded by environmental factors that trigger us to overeat, and we have behavioral processes that impact our ability to follow a diet long-term. (5) When it comes to long-term caloric intake or energy expenditure, generally, no one diet is more advantageous than the other. (5) Even still, many fad diets exaggerate the successful outcomes an individual may experience by following the diet. As fad diets are usually highly restrictive, many are unsustainable for an extensive period. For example, the ketogenic (keto) diet, a dietary pattern characterized by very low-carbohydrate intake, can be challenging to follow due to its restrictive nature. The keto diet failure rate may be high because the diet recommends that only 5 to 10% of calories come from carbohydrates. (8) Achieving ketosis (a fat-burning metabolic state that is the goal of the keto diet) (8) can only be achieved by limiting protein consumption and removing a wide variety of foods, including many higher glycemic whole grains, fruits, and vegetables. (8)

Did you know? About half of the adults living in the United States have a diet-related chronic disease, such as cardiovascular disease, high blood pressure, or type 2 diabetes. Many people use special diets to prevent, treat, or manage these diseases. (14) While weight loss of about 10% of total body weight can have profound positive effects on these diseases, about three-quarters of overweight people are unsuccessful in keeping the weight off after one year. (4)

Biological and homeostatic processes

Research demonstrates that there is more to weight loss than just sticking to diet and engaging in regular exercise. There are physiological responses to weight loss that make losing weight and keeping it off challenging. As a result of weight loss, endocrine (hormonal) adaptations affect energy expenditure and the release of hormones responsible for appetite, causing a person to feel hungrier and less satiated. Increased hunger levels and diminished fullness cues can make achieving weight loss challenging and may even promote weight gain. Two complementary responses, the homeostatic and hedonic pathways, regulate food intake: (7)

The homeostatic pathway controls energy balance, or food intake, by increasing our motivation to eat when energy stores become depleted. Burning too many calories by exercising or failing to consume enough calories due to fasting or following a very low-calorie diet can deprive the body of energy, causing the stomach to release the appetite-stimulating hormone ghrelin. (7)
Hedonic regulation, also known as reward-based regulation, can override the homeostatic pathway even in times of energy abundance by increasing the desire to eat foods that are highly palatable, such as high-fat and high-sugar foods. When consumed, these foods can induce a potent release of dopamine, our “feel-good” hormone, a strong motivator for people to eat even when they are not hungry. (7)

Without us even being aware, our physiological regulation of appetite can impact our perception of our adherence to a diet, even when weight loss has plateaued. The resulting subconscious biases affect our perception of portion control and can lead to intake of larger portion sizes over time. (5) Researchers have investigated the effect that dieting can have on the feedback circuits in the body that control long-term caloric intake. They discovered that individuals who lose weight can experience an increase in appetite by approximately 100 calories (kcal) per day for each kilogram of lost body weight. (5) Weight loss may also decrease energy expenditure by about 20 to 30 kcal per day for each kilogram lost. (5) To help reduce this decline in resting energy expenditure expected to occur after weight loss, resistance training (i.e. weight lifting) is recommended. Resistance training studies have shown significant increases in lean weight and resting metabolic rate as this type of exercise results in greater muscle mass that requires more energy for ongoing tissue maintenance and remodeling. (16) This means that more calories are burned while resting. Furthermore, in a study conducted at the Weight Management Program at the University of Ottawa, researchers demonstrated that weight loss success may depend upon how the skeletal muscle uses oxygen. (6) When the weights of the subjects’ were stable after at least ten weeks on a controlled, strict low-calorie diet, researchers tested biopsies from skeletal muscle and blood samples. The results showed that subjects who responded to the diet experienced weight loss that was 43% greater than subjects who were diet resistant. More weight loss correlated with higher mitochondrial proton leak-dependent respiration (which regulates energy production and affects resting metabolic rate) and a greater abundance of the uncoupling protein, gene UCP3 mRNA, expression (which participates in tissue respiration and energy balance). (6) These results suggest that improved mitochondrial health and function might aid in weight loss because of the effect that increased proton leak and activation of uncoupling proteins have on energy production and the body’s ability to produce heat, and therefore, aid in calorie burning at rest.

Environmental factors

You may have noticed that you consume more food in a social setting, such as during Thanksgiving dinner or a friend’s birthday party. That is likely because our environment can influence many of our choices, especially those that may affect our health.

Our environment can affect our food choices and portion sizes.

Globally, many environmental influences have led to increased physical inactivity and consumption of foods high in calories, fat, and sugar. (9) These changes in activity and dietary patterns are often due to altered environmental and societal changes associated with the development and the lack of supportive policies. (9) Many communities lack grocery stores, gyms, and walking paths, and far commutes for these amenities and places of employment promote vehicle use instead of walking. This “obesogenic environment” includes intense marketing for unhealthy food and increased availability of larger portion sizes of these foods, which impact brain areas related to learning and memory, mood and emotion, and reward. (4) Furthermore, another factor that may influence the diet failure rate is our high-stress society as it can cause people to eat to relieve emotional distress rather than for hunger. (5)

Behavioral processes

Our behavior patterns play a fundamental role in the development of obesity (4) and other diseases. Sustained behavior changes, such as meal planning and self-monitoring, are essential for successful long-term weight loss. (4) A systematic review and meta-analysis of 72 studies suggests that recurrent weight loss attempts may negatively impact body image, pessimistic attributions, and self-concept, leading to feelings of helplessness and predisposing people to failure. (11) Personal motivation, such as from receiving a diagnosis or having a health scare, and self-efficacy, the belief that you can successfully engage in a specific behavior, play a significant role in behavior change. (4) Various behavior change techniques help improve self-efficacy and increase your likelihood of achieving success adhering to a diet or other healthy lifestyle choices. A few examples include:

Action planning
Social support/social change
Prompt self-monitoring of behavioral outcome
Time management (4)

How to adhere to a healthy diet

It’s common for many people to strictly follow a diet during the weekdays, while allowing flexibility on the weekends and special occasions. This can increase exposure to situations that may lead to loss of control with food intake. (17) This excessive food intake on the weekends may be a reason why many diets fail. Maintaining a consistent eating pattern during the weekdays, weekends, and special occasions may contribute to successful weight loss. (17) Exercise and eating breakfast are also important. (17) While exercise helps to burn calories, breakfast consumption may improve micronutrient intake and prevention of eating higher calorie foods later in the day. (16) Regularly eating a balanced breakfast may provide nutrients that allows an individual to have a greater ability to perform physical activity. Research shows that people who maintain weight loss may eat breakfast and exercise more than those who skip breakfast. (16) More recently, studies have demonstrated a number of other factors that may influence our ability to adhere to a particular diet.

Maintaining a consistent eating pattern every day can be helpful for long-term weight loss.

Practice mindfulness and mindful eating

Purposeful, present moment awareness without judgment, also known as mindfulness, has been highlighted in many peer-reviewed articles as a helpful tool for successful, long-term healthy lifestyle changes. A systematic review and meta-analysis investigating how mindfulness-based interventions (MBIs) can affect weight loss and behaviors related to obesity shows that MBIs are moderately effective for promoting weight loss and highly effective for improving obesity-related eating behaviors. (1) For example, practicing mindful eating, also known as intuitive eating, may improve certain maladaptive eating behaviors, such as overeating or eating when not physically hungry for emotional reasons, by increasing awareness of hunger and satiety (fullness) cues. (1) Paying closer attention to the experience of eating also increases taste satisfaction. (1) A tool that is useful to help bring awareness to your level of hunger is The Hunger Scale. (15) It can help you recognize whether you are too hungry, hungry, just right/neutral, satisfied, or too full. Within these five categories, there are two levels to describe your hunger. The scale can also be numbered 1-10, with one being so hungry that you feel starving, and ten being so uncomfortably full you feel nauseous. The ideal range is between 4-6. (15) Using the hunger scale and recognizing your stage of hunger and assessing how you feel during a meal can prevent making unhealthy food choices, eating too fast because you feel famished, or feeling sick from overeating. (15)

The Hunger Scale is a tool used in mindful eating to help bring awareness to hunger and satisfaction.

Paying attention to a meal by using all five senses, slowing down, and taking a moment to consider the rain, sun, harvesting, and the other processes it underwent for the food to get to you is considered mindful eating. (15) This way of eating can help you become more conscious of how, what, when, and why you eat. The BASICS of mindful eating guidelines can be used to become more familiar with integrating mindfulness when eating: B – Breathe and belly check for hunger and satiety before you eat. A – Assess your food. Use your senses and be grateful for your meal. S – Slow down. I – Investigate your hunger throughout the meal. C – Chew your food thoroughly. S – Savor your food. (15) Mindful eating has many benefits. It decreases award-driven eating behaviors, decreases factors that lead to problematic eating behaviors, decreases food cravings, enhances satiety cues and helps you be more in tune with your hunger cues, and increases self-compassion. (2) Instead of some unhealthy foods just being tasty, comforting, and enjoyable, they have become feared. Food phobia seems to be associated with the perception that the food is fattening and will lead to weight gain, and correlates with feelings of guilt. (3) Many mindful eating teachings include removing the labels of “good” and “bad” foods to help individuals get out of the habit of referring to themselves as “good” or “bad” people for eating certain foods. Furthermore, a formal meditation practice combined with informal mindfulness exercises may facilitate weight loss, as meditation can help improve self-regulation. Meditation enhances the ability to redirect attention to the present moment in a non-judgmental and accepting way. It can also help increase awareness of automatic patterns that lead to maladaptive eating behaviors and help individuals disengage from these patterns. In turn, meditation can help with long-term weight loss. (1)

Set SMART goals

For any objective, setting goals should be done in a way that shows a clear action plan to achieve a particular result. Ensuring that your health goals are SMART can help you achieve your desired health outcomes. Your goals should be: S – Specific M – Measurable A – Attainable R – Realistic T – Time-bound (1)

Seek ongoing guidance from healthcare providers

Too often, people are encouraged to lose weight to prevent the onset of disease but lack guidance, especially for the long term. Ongoing interactions with healthcare providers who can provide weight maintenance-specific counseling for at least one year are suggested to yield significant positive outcomes with maintained weight loss. (5) Weight maintenance strategies for long-term success include behavioral strategies such as:

Consuming home-cooked meals
Consuming small frequent meals and snacks throughout the day
Eating breakfast
Increasing physical activity
Practicing portion control
Reducing calorie intake
Reducing screen time
Self-monitoring and self-weighing
Self-monitoring of food intake (5)

Weight maintenance-specific counseling for long-term success needs to appeal to patients’ deeper motives, develop cognitive flexibility, promote cognitive restructuring, provide relapse prevention training, and strengthen satisfaction with the outcome. (5) There is a clear theme present in many research studies regarding people who have achieved sustained weight loss. Continuous self and external monitoring seems to be the golden rule for weight loss and weight loss maintenance and having clear monitoring tools is essential for staying on track, aware and accountable. (12)

The bottom line

The reasons why diets fail are complex and individual. The physiology connected to our internal reward systems can make healthy dietary changes hard to maintain. Environmental and societal changes negatively influence our ability to sustain healthier lifestyle choices as well. Though we cannot control physiology with behavior, sustained behavior changes, including meal planning, self-monitoring, practicing mindfulness, and setting SMART goals, as well as receiving ongoing support from healthcare providers, play a role in sticking to a diet for successful long-term weight loss.

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Why Diets Fail: What the Science Suggests