Why weight loss diets work

Weight Loss
Table of contents:

Energy Balance & Weight Loss

How to Create a Calorie Deficit

Diminishing Returns of a Deficit

What's the Best Diet?

Demystifying the dieting code

Some dieters swear by keto; others by paleo, intermittent fasting, or veganism. Despite the apparent differences in these diverse diets, they can all work to attain weight loss - and it’s not because there’s some magical food you need to eat or remove.

These diets work because they reduce your calorie intake, creating a calorie deficit.

Let’s demystify the dieting code and discuss the science behind weight loss.

Energy Balance & Weight Loss

The first law of thermodynamics states that energy can neither be created nor destroyed: energy can only be transferred or changed from one form to another.

And although this isn’t a physics lesson, it applies to our physical pursuits: in order to lose fat, you must create an energy deficit.

When you provide your body with excess energy, the energy must go somewhere - so if you don’t burn it, you store it primarily as fat. In turn, your body will break down fat to use as energy only when you don’t obtain sufficient energy (i.e. calories) from your diet.

Consequently, there are three possible states for your body’s energy balance…

  1. Calories in = calories out: When your calorie intake matches your body’s energy needs, you’re in a net neutral energy balance and will maintain your current weight.
  2. Calories in > calories out: When your calorie intake exceeds your body’s energy needs, you’re in a net positive energy balance (calorie surplus) and will gain weight.
  3. Calories in < calories out: When your calorie intake falls short of your body’s energy needs, you’re in a net negative energy balance (calorie deficit) and will lose weight.

Throughout the day, your body fluctuates between calorie deficit (between meals) and surplus (upon eating). It’s your average energy balance across time, or “net energy balance” that ultimately determines weight loss, gain, or maintenance.

How your metabolism works

And any diet that accomplishes state #3 naturally results in weight loss…

  • Keto works because removing a whole macronutrient from your diet reduces your calorie intake.
  • Paleo works because restricting yourself to highly satiating, wholesome, and nutrient-dense foods reduces your calorie intake.
  • ⁣⁠Intermittent Fasting works because limiting your feeding window reduces your calorie intake
  • ⁣⁠Zone works because eating tons of vegetables and low-calorie fruits reduces your calorie intake.
  • As for detoxes, lunar, alkaline, and blood type diets…They don’t work or create a calorie deficit - they’re just nonsense.
Diets work by creating a calorie deficit.  It’s not magic, it’s science.

How to Create a Calorie Deficit

You can create a calorie deficit by affecting both sides of the equation: by decreasing your calorie intake and/or increasing your energy expenditure. Let’s dive into each.

Eat less

To reduce your calorie intake, you must eat less than you’re burning. More specifically, you need to limit the amount of macronutrients - that is, protein, fats, and carbs - that you consume. While overall calorie intake determines weight loss, the composition of macronutrients influences what type of weight is lost, such that you lose mainly fat and minimal muscle. When it comes to fat loss goals, typically fats or carbs are reduced while protein is kept fairly high.

Fortunately, you can limit your calorie intake without eliminating entire foods or macronutrients. And, in fact, a more flexible approach to dieting proves more sustainable in the long run. However, because humans are notoriously inaccurate at estimating portion sizes(1), tracking your macros can help ensure you hit the macro and calorie intake needed to achieve fat loss - while leaving space for less nutritious treats in your diet.

To effectively reduce your calorie intake to achieve long-term weight loss, you should also…

  • Prioritize protein to promote satiety and preserve muscle.
  • Get adequate fiber to stay full.
  • Drink plenty of water, since dehydration can mask itself as hunger.
  • Plan your meals ahead and have healthy foods easily available.
  • Eat mindfully and fully chew your food.
  • Focus on whole foods, fruits, and veggies.

Burn more

There are a variety of ways you can burn more calories to create a calorie deficit. Your total daily energy expenditure (TDEE) consists of four different components, each of which can be harnessed to boost your metabolism.

1. Resistance train to increase your resting metabolic rate (RMR): While resistance training isn’t necessary to lose weight, it does support overall health and longevity and is especially useful during weight loss. Muscle tissue raises your resting metabolic rate, as each pound of muscle burns approximately 6 calories at rest, versus 2 calories expended by fat tissue(9). Furthermore, resistance training appears to boost resting energy expenditure independent of muscle gain(10).

To maximize calorie expenditure and preserve muscle during a weight loss phase, aim to train each body part at least twice a week, with a focus on compound lifts, including variations of…

  • Squats
  • Deadlifts
  • Vertical presses (i.e. overhead press)
  • Vertical pulling (i.e. lat pulldown or pull-ups)
  • Horizontal presses (i.e. bench press)
  • Horizontal pulling (i.e. rows)

Resistance training for weight loss is designed no differently than resistance training during maintenance or bulking: use good form, challenge yourself, and strive to get stronger over time.

2. Increase your non-exercise activity thermogenesis (NEAT): NEAT refers to incidental physical activity that occurs throughout the day, in contrast to planned exercise.

NEAT includes activities like…

  • Fidgeting
  • Walking
  • Cleaning
  • Shopping
  • Gardening

Although such activity may seem trivial, NEAT can have an appreciable effect on your metabolism. Of all components of TDEE, NEAT is the most variable and ranges from 100 to 800 calories daily(2) (some research even suggests that NEAT can vary by up to 2000 calories between individuals of similar size(3)). Factors such as occupation, lifestyle, age, genetics, body composition, and energy balance can influence levels of NEAT(4). You can intentionally increase your NEAT through minor lifestyle changes, such as…

  • Taking the stairs instead of the elevator.
  • Parking farther away from the store.
  • Engaging in more active hobbies.
  • Using a standing desk.
  • Going on walks during phone calls.

3. Take advantage of the thermic effect of food (TEF): The food you eat contributes to your energy expenditure as well as your calorie intake: the thermic effect of food refers to the amount of energy required to digest and absorb macronutrients. Protein, in particular, has the highest thermic effect, as your body uses 20-30% of your calories from protein simply to break it down! In contrast, carbs and fats require much less energy to process (5-10% and 0-3%, respectively(8)).

If you want to take advantage of TEF to enhance your energy expenditure, follow a high-protein diet that contains foods like…

  • Lean meat
  • Eggs and egg whites
  • Fish
  • Greek yogurt and cottage cheese
  • Low-fat cheese
  • Quality protein powder
  • Soy products (i.e. tofu, tempeh, edamame)

4. Increase your exercise activity thermogenesis (EAT): Though the effects of exercise on energy expenditure are largely overblown, upping your EAT can provide a modest boost to your metabolism when programmed appropriately. Like NEAT, EAT varies widely depending on the individual - and is affected by changes in body mass and in movement efficiency that comes with repeated practice. As a result, it’s best to use cardio sparingly and to save it for when you reach a weight loss plateau.

High-intensity interval training (HIIT) and low-intensity steady state (LISS) are the most popular forms of cardio used, each of which have their own advantages and disadvantages. While both increase energy expenditure, HIIT workouts burn comparable calories to LISS cardio but in a shorter time period(5). Moreover, HIIT preserves muscle(6) and boosts post-exercise energy expenditure(7) more than LISS. However, the high-intensity nature of HIIT is taxing on the nervous system, can interfere with recovery (and subsequent weight training), and can lead to injury if performed improperly.

If you choose to add cardio during a fat loss phase, incorporate it judiciously, starting with as little as one weekly workout and increasing as needed. Additionally, keep in mind that doing cardio is not a license to eat more and that its metabolism-boosting effects are relatively minor: one hour of low-impact cardio only burns ~300-400 calories, which is comparable to a small snack.

Diminishing Returns of a Deficit

It isn’t always easy to eat less and burn more calories, especially if you’ve been in a severe calorie deficit or dieted for too long. The human body is incredibly adaptive to help us survive in a wide range of conditions, including those of famine. Consequently, your body uses various metabolic adaptations to counteract a calorie deficit, which are advantageous when food is truly scarce but can undermine your weight loss goals. Essentially, metabolic adaptation occurs to minimize your energy deficit so your weight remains stable, and what was once a calorie deficit becomes your new maintenance calories(11). Adaptations arise related to all aspects of TDEE…

1. Unconscious reduction in NEAT: NEAT naturally decreases during a calorie deficit and is further reduced in response to increased exercise, though the extent of this reduction varies across individuals(12, 13, 14, 15). To help counteract this adaptation, you can track your steps daily to ensure you’re consistently moving throughout the day(16) - and add in some walks if you find your step counts unintentionally declining. 

2. Less energy expended during exercise: The more you practice a particular movement (for instance, running(17) or biking), the more efficient your mechanics become, and the less energy you expend to perform that exercise. Losing weight also contributes to less EAT, since it requires less energy to move when you’re lighter; and simply being in a calorie deficit, regardless of weight loss, seems to reduce energy expenditure during exercise(18).  

3. Lower TEF due to lower calorie intake: Lowering your calorie intake inherently leads to a lower TEF, since your body will be processing less food. Nonetheless, by following a high-protein diet you’ll ensure you’re maximizing your TEF as much as possible despite dieting.

4. Muscle loss decreases RMR: Weight loss can involve some degree of muscle loss, which will decrease your resting metabolic rate. Those who start their diet fairly lean are particularly at risk for losing muscle - but even less-lean individuals can lose muscle mass without the proper precautions. 

You can minimize muscle loss by…

  • Losing weight slowly(19)
  • Getting sufficient quality sleep(20, 21)
  • Resistance training(22)
  • Eating a high-protein diet(23)
  • Reducing stress levels(24)

What’s the best diet?

While you can create a calorie deficit both by restricting calorie intake and by increasing energy output, you can only increase your energy expenditure so much - which is why your diet primarily drives the direction of your weight, and why everyone searches for the best diet.  

Ultimately, the best diet is the one you’ll stick with: consistency and long-term adherence are essential to long-term weight loss(25).

For most people, the best, most sustainable diet will have a few common features. In general, the best diet is one that…

1. Is flexible: Eliminating entire foods or food groups is rarely sustainable - and forbidding yourself from consuming foods that you like creates a restrictive mindset that often fosters an unhealthy relationship with food(26). Learning to appreciate all foods and eat anything in moderation will make your diet more enjoyable and easier to keep up as a lifestyle.

2. Includes adequate protein: Protein has numerous benefits, from promoting satiety to building and preserving muscle. Following a high-protein diet will not only prevent overeating but also ensure you attain the body composition you desire(27).

3. Emphasizes whole foods: Whole foods like meat, veggies, and fruit are both nutritious(28) and satiating(29) and thus should be a cornerstone of any sustainable and healthy diet. While highly processed foods are fine in moderation, they’re highly palatable, more calorie-dense, and less filling, which can predispose overconsumption.

4. Fits your lifestyle: A diet that doesn’t fit your lifestyle will never last. If you find intermittent fasting or time-restricted eating works for you, go for it! If you prefer eating larger, less frequent meals throughout the day, do it! Every body and life is different, so consider your personal preferences and schedule when determining the right diet for you.

Lastly, it’s important to realize the role of small steps and habit formation in sustainable weight loss and dieting. Radically overhauling your current diet due to a burst of motivation is often too dramatic a shift to keep up. Instead, consider making smaller, more do-able tweaks to your nutrition and maintaining them over time, so you develop habits. In the end, your day-to-day behavior depends more on habits than willpower, so making healthy choices automatic simplifies the dieting process and supports lasting results(30).

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