Effective Diet to Lose 20 Pounds? Guide

A few years ago (already!), I wrote an article here dealing specifically with weight loss in children and teenagers, as I was working as a physiotherapist with several families who had asked me questions on the subject.

Today, I’m focusing more specifically on adults looking for an effective diet to lose 20 pounds (or 40 pounds, etc./the reasoning is the same). Because this is the problem I have most often encountered with my patients, who ask me for advice on how to lose weight.

I’ll try to give you as much reliable information as possible on this subject. Based on my own experience, but above all on the results of the hundreds of scientific studies that exist on the subject, to see what works best in the long term for weight loss.

If you have any questions or comments, or if you’d like to share your experience, feel free to comment!

♻️ Last update: May 5, 2025.
👩‍⚖️ Declaration of financial interests: none directly related to the subject. My complete declaration of financial interests is in the legal notice section.
Written by Nelly Darbois, physiotherapist and scientific editor

Why lose 20 pounds?

I’m only writing this article for people who absolutely want to lose 10, 15 or 20 pounds, whatever their motivation. And who are overweight or obese.

So I’m not going to reiterate the physical and mental health benefits of having a weight relative to your height that’s “within the norm” (Body Mass Index between 18 and 25 for an adult).

My aim here is absolutely not to convince you to lose weight, whatever your current weight. Some people may consciously decide they don’t want to lose weight.

My aim here is not to convince people to lose weight. It ‘s just to give some pointers for those of you who want to, whatever your motivations.

Why yet another article on the web about effective diets?

For over 4 years now, I’ve been writing content every day for my website, Fonto Media, which you’re currently visiting. Mainly about health.

And I’ve never dealt with the subject of “how to lose weight” before, apart from an article on weight loss in children and adolescents. And yet:

• as a physiotherapist for 11 years, I was in almost daily contact with people who wanted to lose weight and asked me for help;
• I have accompanied several people on this quest;
• I’ve read several books and scanned dozens of academic and scientific publications on the subject;
• I often refer to Michel Desmurget’s book: L’anti-régime : maigrir pour de bon, which is by far the most rigorous content I’ve read on the subject.

Many of my patients gave me good feedback on this book. But for many of them too, it was a rather arduous, dense read. And it was difficult to extract relevant, step-by-step information. The same goes for the latest, supposedly more practical version of the book, L’anti-régime au quotidien, which I also find less rigorous in its approach.

My aim here is to offer you something more practical. And without proposing a “miracle diet” or grandmother’s remedy for losing weight fast, because our scientific knowledge of weight gain and loss unfortunately does not suggest that such solutions exist.

The 4 most important things to keep in mind before starting a diet

Here are the 4 main principles of weight loss that I find are not so well known when I discuss the subject with people I meet.

1. The faster you lose weight, the faster you gain it back (and more pounds).

You’ve probably heard of the yo-yo effect: people who lose weight quickly tend to put it back on quickly, often with extra pounds,

Why?

• When you lose weight fast, your basal metabolism (the amount of energy your body burns at rest “doing nothing”) slows down.
• This happens because your body perceives a sudden reduction in calorie availability and reacts by saving energy.
• When you regain weight, even at a normal rate, your metabolism may remain slower, meaning you burn fewer calories at rest and during exercise, which can make it harder to maintain weight loss.

There are also other mechanisms behind this, notably psychological. The highly restrictive diets often required to lose weight quickly can be difficult to maintain over the long term. Once you stop following these diets, you may revert to previous eating habits, which can lead to weight regain.

Perhaps you’re telling yourself that your willpower is strong enough not to fall into this trap. Unfortunately, even the most motivated people are affected by the limitations of diets that make you lose weight too quickly. It’s all biological and physiological, not psychological, and it’s not a question of willpower.

2. It’s all a question of balancing inputs and outputs

When we think of “diet” or “weight loss”, we often think first and foremost of our diet. We think that the main lever for action is to reduce the number of calories we consume each day.

This is partly true, but only partly.

Why do you ask? Because you also have to take into account the calories you burn, the calories you eliminate!

Even “doing nothing” (for example, sitting or lying down all day), our body eliminates calories every day. But as soon as we become active (for example, by standing or walking outside), we burn more calories.

When you’re trying to lose weight, you need to strike a balance between what you eat and drink (= calories in = calories out) and what you burn (= calories out = calories in).

If you focus on just one of these levers, it may not work as well. Many people ask “how can I lose weight quickly without practising sport?” It’s possible, because increasing your level of physical activity doesn’t necessarily mean practising sport.

It may simply mean being a little more active in your daily life, for example by walking a little more often (see also: tips for walking more often).

You’ll always find best-seller authors who argue the opposite. For example, science journalist Gary Taubes, in Pourquoi on grossit : les vraies causes du surpoids, les vraies solutions. In his view, it’s nonsense to say that you get fatter because you consume more calories than you burn.

To cut a long story short: even if his rhetoric is seductive, it runs counter to what has been the consensus in international scientific literature for several decades. If you’re interested, I’ve included an article at the end of this article that explains this more fully!

3. Quantifying everything you eat is often necessary

Even if it’s very restrictive, to really know where you stand and see if you’re balancing your inputs and outputs, you’ll probably need to estimate the calories you swallow each day. But also, estimate how much energy you’re expending.

There are free smartphone applications that make it easy to do this. Of course, you can also do it the old-fashioned way in paper format, which is just as good!

See also: Can you eat only once a day?

4. Reduce the calories you consume just a little.

Here’s what our current scientific knowledge on weight loss tells us. I’m quoting from the summaries produced by Michel Desmurget, a neuroscience researcher who has studied the subject of dieting.

Don’t worry: I’ll then “translate” these words into what they mean in concrete terms 🙂.

Thus, a deliberately cautious assessment of the data in the scientific literature indicates that it is possible to reduce your usual caloric intake by 15% without arousing any detectable metabolic compensation or increased feelings of hunger. In concrete terms, this means thatby eating 15% less each day than you did initially, you can lose weight substantially, comfortably and permanently.

Michel Desmurget, L’anti-régime

It therefore appears possible to increase energy expenditure by 20% over the long term , without the body significantly increasing its caloric intake in compensation.

Michel Desmurget, L’anti-régime

So, for those wishing to lose weight effectively, the best option is to combine a prudent reduction in calorie intake with a measured increase in physical activity. In total, the calorie deficit resulting from this combination should not exceed 25% of the initial calorie count. The distribution of this imbalance over its various bases can be achieved in any way, provided that the total deficit in inputs does not exceed 15% of the total and the excess in outputs does not exceed 20%.

Michel Desmurget, L’anti-régime

Doesn’t that tell you a lot? That’s normal: I too needed a lot of time to read and reread all this and to do additional research to understand it properly.

Below, I’ll try to make things clearer by telling you what to do if you want to follow this method.

Here’s how to do it in 5 steps. If you’d like me to create an even more helpful/simple ebook on the subject, let me know in the comments, and I’ll gladly devote some time to it.

1. Set a goal: how many pounds do you want to lose?

Let‘s start with the idea that you want to lose 20 pounds. I’ll then explain how to calculate how long it will take you to lose those 20 pounds using these principles.

2. Calculate your current weight and calorie expenditure

The best way to find out your weight is to weigh yourself at least 7 mornings in a row, and then average your weight over these 7 days.

Then use an online calculator (like this one) to find out how many calories you consume each day.

After clicking on Calculate caloric intake, you’ll see the following:

Take the highest figure given in “Stabilizing your weight”. For example, for me, 2110 kcal.

This means that if I maintain my current level of physical activity (rather sedentary job sitting in front of the computer to look after Fonto Media, but lots of daily walking to compensate, and running several times a week), I’ll keep my current weight by eating around 2110 kcal a day.

3. Calculate your calorie expenditure and target physical activity level

If we follow the main principles I’ve talked about, to lose weight, we’ll have to stay away from those 2110 kcal/day (for me; you have your own figure, see above). But be at less.

Ideally, this should not be done “by the ladle”, but targeted at 25% less.

• If I want to play on diet alone, I’d have to consume only 1582 kcal per day. (Calculation: 2110-(2110*(25/100)))
• But by doing so, we know that it may be too restrictive for our bodies.
• So we’re going to start by increasing our physical activity a little. For example, we’ll increase physical activity by 10% compared to the current level (we’ll see what that means in concrete terms later). And then we’ll have to reduce our food/drink intake by only 15% instead of 25%. This still gives my basic figure of 2110 kcal (use your own for the calculations; and if you can’t do the maths, leave me a comment with your figure, I’ll do it for you!
  • 1793 kcal: I can eat and drink the equivalent of 1793 kcal every day;
  • 211 kcal: I’ll need to burn 211 kcal more every day than I do now. That’s 1 hour more walking/day than I do now, if I do it at a slow pace. (You have calculators to work this out).

4. Implement this in your daily life

Now you’ll have to translate this:

• 1793 kcal, so what can I eat/drink? For me, the easiest way is touse free apps (my favorite: FatSecret). You enter your food items one by one, the quantities, and that gives you the kcal. It’s pretty easy to learn. And as time goes by, you’ll need to do it less and less, and you’ll have a better idea of the calories you’re consuming;
• 211 kcal, what does that mean in terms of physical activity per day? Likewise, there are apps that do this (like Fatsecret), or online sites that offer calculators or tables to find out how many calories you consume according to your weight, physical activity, intensity and duration.

5. Weigh yourself at least once a week and take stock after a month.

Ideally, weighing yourself every day allows you to estimate your weight much more reliably. Because our weight fluctuates enormously from day to day, even if we always weigh ourselves at the same time.

If this isn’t too much of a strain for you, I recommend weighing yourself every day, and averaging your weight every week.

After a month, you should already start to see a small weight gain, of at least a few hundred grams (if not much more).

Dietary supplements such as Reduslim and Matcha Slim are not useful for weight loss.

How long does it take to lose 20 pounds?

To maximize the chances of achieving your weight loss goal, ideally your objective should be as clear as possible. But also achievable and realistic!

I assume that your goal is to lose weight sustainably, over the long term. It’s up to you to readjust your goal if you’re not on track!

Let’s take a (true) example of one of my patients whom I accompanied in this process (I was originally seeing her for her knee replacement rehabilitation).

Mrs. S is 53 years old, weighs 160 pounds for 1m60, and it’s partly her moderate obesity (BMI = 31) that led her to undergo prosthetic surgery at a relatively young age for osteoarthritis of her knee. She is afraid of daily physical activity. This means that she needs 1810 kcal/day to maintain her weight.

She also has pain in her other knee, and is increasingly restricted in her activities because of her weight. She has already tried countless diets, with and without methods, with and without a nutritionist or dietician, with a stay in a weight-loss spa in term, and a month’s stay in a specialized rehabilitation center.

At best, she has managed to lose a few pounds, but has always put them back on (not necessarily more, though). However, she still wants to try and lose 20 pounds.

Objective:

• lose 20 lbs, so reach 140 lbs;
• calories per day: 450 calories less than at present (25%), i.e. :
  • 250 fewer calories consumed per day than the usual 1,810 per day;
  • 200 more calories burned every day by increasing physical activity;
• it will take 6 months to reach this goal.

How do you calculate this? This is surely the most complex calculation. I’ve used some not-so-easy-to-use tools for this, and haven’t found an easy-to-use equivalent to date. For mathematicians: use the Wishnofsky constant.

If you know of any, leave me a link in the comments. And if you don’t know any, but you’d really like to have access to this, leave me your figures in coordinates, and I’ll do the math for you. To do this, you need to tell me (even anonymously) :

• your current weight ;
• the weight you want to lose (e.g. 10 lbs, 15 lbs, etc.);
• your current daily caloric expenditure.

Because it’s much nicer not to go blindly forward and to know concretely where you should be at the end of 3 months, 6 months, to know if you’re on the right track, or if you need to readjust something!

Is it more effective to have someone help you lose weight?

There are dozens and dozens of studies evaluating the most effective long-term medical, paramedical (psychologists, nurses, dieticians, physiotherapists, etc.) and surgical treatments to help people lose weight.

The following is a summary of international recommendations from countries around the world:

• implement a multifactorial, comprehensive lifestyle program, including reduced caloric intake, increased physical activity and measures to support behavior change for at least 6 to 12 months;
• offer bariatric surgery (e.g. gastric banding, sleeve gastrectomy) only when non-operative procedures have failed and for people with a BMI over 35.

Source : Semlitsch 2019

However, the effectiveness of these supervised programs (for example, in a specialized center, or by a dietician or nutritionist in private practice) compared to implementing these habit changes on your own has not been evaluated. Quite simply because it’s complicated to include people who do this on their own in studies!

***

You’ve reached the end of this article dedicated to “rational” and sustainable weight loss. I’m aware that there are surely some things that are still unclear or confusing: I suggest you leave a comment if that’s the case, explaining what you haven’t understood or what you’re missing.

I’ll update the article accordingly, until I come up with a version that’s more satisfying and understandable for most people!

I’ve written other articles on weight loss. Mainly to give reasoned opinions on devices or remedies often presented as “miracles”, when it’s reasonable to think that they have no significant effect: Reduslim, Matcha Slim, magnetic bracelets, etc.

See also :

Articles similaires