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The Science Behind Dieting, and Why it Doesn’t Work

By Lisa McCormick, FNP-BC, RD, CDCES

This edition covers:

  • Why fad (or strict) diets can reduce weight, but only in the short term.
  • How the body is physiologically programmed to regain weight using hormonal signals.
  • The five principles of sustained weight health.

According to an October 2023 Forbes Health survey, 34% of people say losing weight is their goal for 2024, while 32% plan to improve their diet. However, the average resolution lasts approximately three months. Is that enough time to achieve and sustain impactful weight loss? When it comes to how we eat, the answer is: it depends.

Whether it’s keto, the latest “detox” trend, or the cabbage soup diet (anyone else fall prey to that in the ‘80s?), many trending diets are effective at initial weight loss, but are not sustainable over the long-term. As a newly minted dietitian practicing in the mid-1990s, I repeatedly saw the yo-yo of weight gain and loss. Many of my patients were looking for the golden ticket “diet” and wanted the weight loss to happen fast. I remember being struck by how quickly weight would come off with any number of rigid “diets”, and then how much more quickly that weight returned once the rigid “diet” stopped.

While people often attribute these weight ups and downs to “failed diets”, science and data provide more context behind this phenomenon in terms of physiology and behavior change.

The Physiology of Hunger and Fullness

Navigating the world of weight loss — and sustaining said weight loss —  can be frustrating at best, especially when it involves understanding the body's hormonal signals. Let’s break it down.

The stomach and brain are partners in managing hunger. When the  stomach empties, it produces a hormone called ghrelin, often referred to as the "hunger hormone." Ghrelin sends a message to the brain saying, "let’s eat!" But that’s not all. Fat tissue produces another hormone called leptin, known as the "fullness" or “satiety” hormone. Leptin's role is to tell the brain you're full.

Now, here's where it gets tricky. With weight loss, the body's metabolism actually slows down. There is a decrease in circulating leptin, making the body feel less full than before. Meanwhile, ghrelin levels rise, causing an increase in hunger. It's as if the body is conspiring to regain the weight it lost.

As discouraging as that sounds, it’s worth mentioning that hunger isn’t the only reason we eat. Cravings, emotions, stress eating and more are also at play, as are the foods available to us in our environment. So while it is important to understand the hormonal changes as part of the bigger picture, it isn’t the entirety.

Here’s the good news  – we’re still in the driver’s seat ! While it's true that our bodies adapt, making sustained weight loss more difficult, with healthy behavior change and support, weight loss can be maintained successfully. It's about understanding the physiological post-weight loss changes, and related behaviors, and then working with them, not against them. Lifelong weight health is both achievable and sustainable with perseverance and the right strategies.

The Complexity of Behavior Change

Successful weight management requires embracing enduring behavioral changes rather than relying on the latest fad diet. However, changing behavior can be a complex endeavor based on the individual’s personal barriers.

In a 2021 study examining the relationship between emotional eating and obesity, emotional eating was found to be more common in individuals with obesity (43.5%) compared to participants considered normal weight (33.5%) and underweight (18.4%).

Behavioral health conditions also affect patients’ ability to follow through on critical self-care measures, such as medical appointment attendance, diet and nutrition, medication adherence, exercise, and self-monitoring of blood glucose or blood pressure.

To overcome these challenges and be successful with long-term weight health, research shows that ongoing support is key. So much so that the American Diabetes Association advises that people who have lost weight participate in a long-term (>1 year) comprehensive weight management program.

The combination of physiology and behavioral complexity is why fad diets aren’t effective in the long-term, and why achieving sustained weight health is highly individualized and requires long-term support.

Five Principles of Sustained Weight Health

There is no one-size-fits-all diet that guarantees successful long-term weight management. Illustrating this, a recent survey of 1,658 Omada members found that those who lost more than 5% of their weight since starting the program preferred intuitive/mindful eating over stricter alternatives, such as low-carb and intermittent fasting diets.

Sustained weight health requires a combination of five principles:

1. Adherence

Long-term weight health hinges on the ability to adhere to new behaviors. Choose an eating plan that's both effective in the short-term, and realistic and flexible enough for the long run.

2. Lifestyle Alignment

To truly achieve and sustain weight health, a nutritional plan can’t be a fleeting “what’s the newest diet” intervention; it must blend into the individual’s lifestyle, which includes personal preferences, cultural background, access and affordability of foods, as well as any specific nutritional needs. A sustainable diet resonates with one’s lifestyle, becoming an integral component of their daily routine.

3. Caloric Reduction

We cannot avoid the need to reduce calories to sustain weight loss. Post-weight loss metabolic adaptations are real, and calorie needs decrease significantly. For most people, this requires cutting daily intake by 300 to 500 calories, and sustaining this reduction over the long-term, regardless of which type of diet is followed.

4. Physical Activity

While it might not be part of a diet, it bears mentioning: physical activity is essential for metabolic health, preserving muscle mass, and boosting overall well-being. Research suggests at least 150 to 300 minutes a week of moderate exercise, along with regular strength training, is needed to sustain weight loss.

5. Support Systems

Support is the secret sauce of long-term success. Whether it's the support of family, friends, or the Omada community, social support provides the accountability and encouragement you need.

While it’s possible to lose weight with any number of short-term fad diets, to achieve the more elusive goal of sustained weight loss, we have to look beyond rigid eating habits or adhering to the rules of one specific dietary plan.

Science and data (along with real life experience) tell us the path to long-term weight health requires behavior change that counteracts the metabolic adaptations of weight loss.

This is a journey and not a sprint, and like any journey, it can be made easier – and more enjoyable – with reliable social support.

This Proof Points edition was originally published on LinkedIn on 1/19/24.