How to lose weight: the definitive science-based guide (2026)

The physiological truth: why losing weight is simple but not easy

Losing weight is a thermodynamics problem. If you consume less energy than you expend, your body uses its reserves (mainly fat) as fuel and you slim down. This first law has been confirmed in hundreds of metabolic chamber studies — the gold standard for measuring energy expenditure — including the seminal one by Hall et al. published in The Lancet in 2011. There are no hormonal exceptions, no "broken" metabolisms that violate physics, no magic foods that make calories not count. What does exist are factors that make creating that deficit more or less difficult: hunger, cravings, social friction, fatigue, stress, sleep deprivation, thyroid hormones, medications, previous dieting history. And that is where most people fail — not in physiology but in sustainability.

One data point that sums up the problem: 85% of people who lose weight regain at least 80% within the following 5 years according to long-term follow-up by the American Psychological Association. The cause is not lack of willpower — it is that most strategies are unsustainable by design. 800-kcal diets, binary restrictions ("no carbs"), plans without exceptions for social events. All of that produces fast loss and guaranteed rebound. The weight loss that sticks is the one you can maintain on any given Tuesday without thinking about it, 5 years from now, when the initial motivation is gone. This guide is written for that goal.

Calculate your starting point: TDEE, body composition and realistic goal

Before subtracting calories you need to know how many you expend. Your Total Daily Energy Expenditure (TDEE) is made up of four parts: Basal Metabolic Rate (BMR, 60-70% of the total), the thermic effect of food (TEF, 10%), voluntary physical activity (EAT, 5-15%) and non-exercise activity thermogenesis (NEAT, 15-25% — walking around the office, moving, fidgeting). The most accurate formula used in clinical research is Mifflin-St Jeor, published in 1990 and validated since then in over 20 comparison studies.

• Men: BMR = (10 x weight kg) + (6.25 x height cm) - (5 x age) + 5
• Women: BMR = (10 x weight kg) + (6.25 x height cm) - (5 x age) - 161
• Multiply BMR by your activity factor: Sedentary (desk job, no exercise) = 1.2, Light (exercise 1-3 days) = 1.375, Moderate (3-5 days) = 1.55, High (6-7 days) = 1.725
• The result is your TDEE: the calories you need to maintain your current weight

A numeric example you can copy

Maria, 34 years old, 68 kg, 164 cm, trains 3 times per week. BMR = (10 x 68) + (6.25 x 164) - (5 x 34) - 161 = 680 + 1025 - 170 - 161 = 1374 kcal. TDEE = 1374 x 1.55 = 2130 kcal. If she wants to lose weight, her target is 1630-1830 kcal/day (300-500 kcal deficit). At that rate she will lose 0.3-0.5 kg/week, about 1.5-2 kg per month. To dig deeper into the exact mechanics of the deficit, read our caloric deficit guide for beginners, which explains why 300-500 kcal is the optimal range and not more.

The caloric deficit: how much to cut without stalling your metabolism

This is where most people get it wrong in both directions. Some undershoot (100-150 kcal deficit) and the loss is so slow they quit in two months out of frustration. Others overshoot (800-1000 kcal deficit) and trigger metabolic adaptation: their body lowers BMR, spontaneously reduces NEAT (fewer daily steps, less fidgeting), raises hunger, increases cortisol and generates rebound as soon as they relax the plan. The sweet spot according to evidence is 300-500 kcal/day for most people, or 20-25% below TDEE for people with significant excess weight who can tolerate larger deficits without consequences.

Metabolic adaptation is real. Fothergill et al. (Obesity 2016) followed 14 Biggest Loser contestants and found their BMR was still 500 kcal lower than predicted by their new weights, six years after the show. Losing weight fast with an aggressive deficit permanently damaged their metabolism. The lesson: go slower than you would like. 0.5-1% of your body weight per week is the sensible upper limit. For an 80 kg person that is 400-800 grams per week — nothing to impress Instagram with but something that sticks long term. If you go more than 3 weeks without losing weight on the same deficit, don't cut more calories: recalibrate your TDEE (you now weigh less and expend less), increase activity, and check whether you're really eating what you think you are. In how to count calories without going crazy we explain the 7 most common underestimation mistakes.

High protein: the anti-flabbiness insurance during weight loss

Protein is the most important macronutrient during any weight loss — not because of metabolic magic, but because of three concrete mechanisms. First, it preserves muscle mass when you eat less than you expend. Without enough protein, your body uses muscle as fuel because it is easier to break down than fat, leaving you with the same body but smaller ("skinny fat" effect). Second, it has the highest thermic effect: your body spends 20-30% of protein calories just digesting it, compared to 5-10% for carbs and 0-3% for fats. Third, it is the most satiating macro: one gram of protein reduces hunger more than a gram of any other macro according to the Holt et al. satiety index.

The figure to target during an active caloric deficit is 1.6-2.2 grams of protein per kilo of body weight, according to the ISSN consensus (Jäger et al. 2017). For a 65 kg woman that is 104-143 grams per day, distributed across 3-5 servings of 25-40 g. For an 85 kg man that is 136-187 grams. If this sounds like a lot, it is: the general population typically eats 0.8-1.2 g/kg, which is enough to survive but not to lose fat while preserving muscle. The definitive evidence comes from Longland et al. (Am J Clin Nutr 2016): men who did an aggressive caloric deficit with 2.4 g/kg of protein and strength training gained 1.2 kg of lean mass while losing 4.8 kg of fat in 4 weeks. For practical source distribution and timing, read how much protein do you need per day with the full calculator by goal.

Choose your carbs and fats based on your activity level

Once total calories and protein are fixed, carbs and fats are flexible. Low-carb, low-fat, Mediterranean and vegan diets produce the same weight loss when calories and protein are equalized, according to the famous DIETFITS study by Gardner et al. (JAMA 2018) with 609 participants over 12 months. What matters is that you can stick to the diet. That said, there are useful guidelines: if you train strength intensely, prioritize more carbs (4-6 g/kg) to refill glycogen; if you are sedentary or train lightly, you can go lower on carbs (2-3 g/kg) and higher on fats. Fats should stay between 0.6 and 1.2 g/kg to protect hormonal function: below 0.5 g/kg for weeks, testosterone and estrogens drop significantly.

• Recommended carbs: oats, rice, potato, whole fruit, legumes, whole-grain bread with fiber >6 g/100g
• Healthy fats: extra virgin olive oil, avocado, nuts, oily fish (salmon, sardines, mackerel), egg yolk
• Minimize: added sugars, refined seed oils in excess, ultra-processed foods with >8 ingredients
• Fiber: aim for 25-35 g/day (WHO recommends a minimum of 25 g). Increases satiety, improves digestion and reduces insulin spikes

To understand what each macro really is and how your body processes them, we have a full guide at protein, carbs and fats: macronutrient guide. And if you want to learn to read nutrition labels so you do not fall for "healthy" products that are disguised caloric bombs, check out how to read nutrition labels.

Exercise: how much strength and cardio you actually need

Exercise is not the main lever for losing weight — diet is. The evidence is unequivocal: a meta-analysis by Thomas et al. (Obes Rev 2012) with 1,847 participants found that exercise alone (without changes in diet) produces an average loss of only 2-3 kg in 6-12 month programs. The reason: burning 300 kcal running is relatively easy, but it is trivial to compensate with an extra snack you "earned" by training. However, exercise is crucial for three reasons that have nothing to do with direct expenditure: it preserves muscle mass, improves insulin sensitivity, and increases basal energy expenditure long term.

The optimal recommendation combines strength and cardio. For strength: 3 weekly sessions of 45-60 minutes focused on compound movements (squat, deadlift, bench press, row, pull-ups, military press). For cardio: 150 weekly minutes of moderate intensity (brisk walking, cycling, light jogging) per WHO and ACSM, spread across 3-5 sessions. If you're starting from scratch, our gym routine for beginners has a 3-day/week plan with minimal gear (dumbbells and a resistance band). And if you wonder which burns more, the debate is settled: combining them always wins. Read cardio vs weights: which is better for losing weight with the full scientific breakdown.

The invisible lever: daily steps

Far more important than your gym session are your daily steps. NEAT (non-exercise activity) represents between 200 and 800 kcal/day of variability between people. Going from 3,000 to 10,000 daily steps can add 200-300 kcal of automatic expenditure without you noticing it as "exercise". It is the most underrated lever of weight loss: walking after meals, parking far away, using stairs, getting up every 30 minutes if you work seated. A basic smartwatch that tracks steps is one of the best investments you can make.

Sleep, stress and hormones: the invisible factors

You can have the perfect diet and an impeccable exercise routine, but if you sleep 5 hours a day you are going to sabotage your weight loss. The classic study by Spiegel et al. (Ann Intern Med 2004) showed that sleeping 4 hours for 2 nights increases ghrelin (the hunger hormone) by 28% and reduces leptin (the satiety hormone) by 18%. Translation: your body asks for more food, especially sweet and carb-heavy, and you never feel full. A later study by Nedeltcheva et al. (Ann Intern Med 2010) with controlled caloric restriction showed that people sleeping 5.5 hours lost 55% less fat and 60% more muscle mass than those sleeping 8.5 hours — eating exactly the same calories.

Chronic stress is the other invisible lever. Persistently elevated cortisol (toxic job, personal problems, insomnia, overtraining) promotes abdominal fat storage, increases emotional hunger and worsens sleep quality, creating a vicious cycle. To dig into how to sleep better for weight loss, read how sleep affects your weight, and for the cortisol-adiposity connection stress, cortisol and weight. And if you notice you eat without real physiological hunger (nighttime snacking, eating from anxiety or boredom), our guide emotional hunger vs real hunger explains how to tell them apart and break the pattern.

The visual plate: the universal rule that works without scales

Counting calories is the most precise tool, but not everyone wants to live with an app open. For those cases there is the Harvard Healthy Eating Plate rule, one of the most validated visual guides, used by diabetes prevention programs worldwide. The rule: half the plate is vegetables and fruits (not counting potatoes), a quarter is lean protein (chicken, fish, eggs, legumes, tofu), and a quarter is whole grains (brown rice, quinoa, whole-grain pasta, bread with fiber). Olive oil as main fat, water as main drink. This simple rule, applied to 2-3 meals a day, automatically generates a moderate deficit for most people with excess weight without having to weigh anything.

The advantage of the visual method is adherence: it requires no equipment, works in restaurants, and generates no anxiety over exact figures. The disadvantage is precision: if your problem is that you already eat "healthy" but are not losing weight (because oil, nuts and cheese can add 500 invisible kcal), you need to track. The ideal combo is to use the visual plate as a general rule and track 2-3 days per week with an app to verify you are in a deficit. With weekly meal prep for beginners you can prep the components of the plate (cooked proteins, roasted vegetables, grains) on Sundays and assemble meals in 5 minutes during the week.

The 10 mistakes that keep people from losing weight

After analyzing thousands of real logs in Renzy, these are the patterns that repeat among people who "do everything right" but see no scale results:

• Underestimating calories by 20% to 50%. The classic study by Lichtman et al. (NEJM 1992) measured real vs reported intake and found that people with obesity reported eating 1,028 kcal less than they actually ate. An honest weighing (not "a handful of almonds" but 25 g exactly) is revealing
• Not counting caloric drinks. A latte with sugar (150 kcal), a glass of orange juice (110 kcal), a glass of wine (125 kcal), a beer (150 kcal). Two drinks a day are 300 invisible kcal that can wipe out the entire deficit
• Being disciplined Monday through Friday and going off the rails Saturday and Sunday. If your weekly deficit is 3500 kcal (500/day), one Saturday with 1500 extra kcal reduces it to 2000, and a similar Sunday wipes it out completely
• Following very restrictive diets that generate rebound. 800-1000 kcal diets work the first 3 weeks but trigger so much hunger that 95% of people rebound. Better a 20% deficit sustainable for 6 months than a 40% one sustainable for 6 weeks
• Weighing yourself only once a week (or worse, every day) and reacting to the number. Weight fluctuates 1-2 kg from water retention, salt, hormonal cycle, bowel contents, glycogen. Use the weekly average, not the Tuesday reading
• Not doing strength training, thinking you only need cardio. Losing weight without strength makes you small and flabby, not athletic. The "just run" formula is the skinny-fat recipe
• Obsessing over "clean eating" instead of calories. One hundred grams of almonds (578 kcal) are more caloric than a medium burger. Natural is not a synonym for low-calorie
• Not sleeping enough. Less than 6 hours sabotages hormones, hunger, recovery and motivation. It is literally impossible to lose weight optimally while sleeping badly
• Not drinking enough water and confusing thirst with hunger. Read how much water should you drink per day for the exact figure by body weight
• Giving up at 4-6 weeks because "I see no results". Visible results arrive at 8-12 weeks; what happens before is biochemistry in progress. Consistency is the only variable that matters long term

5 viral myths about losing weight that science has debunked

The internet is full of advice that sounds convincing, is repeated millions of times on TikTok, and does not survive a single peer-reviewed paper. These are the five most common, with the evidence that takes them down:

Scientific comparison: the 5 most popular diets for weight loss

Keto, Mediterranean, intermittent fasting, high-protein, vegan. Which works best? The science is clear: when calories and protein are equalized, all produce similar loss. The real difference is in sustainability, fit with your life and contraindications. This table summarizes the evidence and helps you choose without ideology:

The lesson: the best diet for you is the one you can sustain for 12 consecutive months without suffering. The Mediterranean diet wins on most health and adherence metrics, but if you already know that skipping dinner works well with your routine, intermittent fasting is legitimate. To dig deeper into one of the most popular options, read the complete guide to 16:8 intermittent fasting with a step-by-step protocol.

Your 30-day plan to start today (step by step)

If everything above overwhelms you, these are the eight concrete steps that cover 90% of the result. Follow the order, do not skip any, and add only one new one per week until you have them all in place:

1. 1

   Day 1-2: Calculate your TDEE

   Use the Mifflin-St Jeor equation with your weight, height, age and activity multiplier. Subtract 400 kcal from the result. That is your daily caloric target for the next 4 weeks.

2. 2

   Day 3-4: Set your protein and shop 4 base sources

   Multiply your weight by 1.8 g/kg. Buy chicken, eggs, 0% Greek yogurt and lentils or tofu. That covers the 4 main meals of the week.

3. 3

   Day 5-7: Start tracking with an app

   Download Renzy or another app with photo scanning. Log 80% of what you eat. Do not try to be perfect — try to be consistent. Look for the trend, not the exact number.

4. 4

   Day 8-14: Add 3 strength sessions per week

   Follow the gym routine for beginners. Monday, Wednesday and Friday. 45 minutes. No excuses: you can do it in the living room with two dumbbells.

5. 5

   Day 15-21: Protect your sleep

   Set a bedtime and wake time (same weekdays and weekends). Screens off 1 hour before. Bedroom at 18-20 degrees Celsius, blinds closed. If you sleep less than 7 hours, this is more important than anything else.

6. 6

   Day 22-25: Add 8,000-10,000 daily steps

   High NEAT = 200-400 kcal/day extra without structured exercise. Park far away, use stairs, walk after meals, stand up every 30 min if you work seated.

7. 7

   Day 26-28: Measure real progress

   Weigh yourself fasted 3 times/week and use the average. Front and side photo in natural light. Waist measurement at the navel. Record everything. Being disappointed by the daily scale is the fast track to giving up.

8. 8

   Day 29-30: Recalibrate and plan month 2

   Recalculate your TDEE with your new weight. If you lost 1.5-3 kg, keep going. If you lost less, review caloric underestimation. If you lost more than 3 kg, raise by 150 kcal to avoid metabolic adaptation.

3 real cases with numbers (so you see how it works in real life)

Theory is nice, but results are what matter. These are three real anonymized cases of Renzy users who completed at least 6 months of tracking:

Case 1: Anna, 38, moderate weight loss goal

Starting point: 78 kg, 162 cm (BMI 29.7 — overweight grade II), sedentary, 2 young children, limited time. Calculated TDEE: 2100 kcal. Target: 1700 kcal + 125 g protein + 8,000 steps/day + 2 home strength sessions of 30 min. Result at 6 months: 67 kg (-11 kg), waist -12 cm, 3 consolidated workouts/week. Key to her success: Sunday meal prep + tracking only via photo (without weighing food). She dropped the idea of perfection and consistently captured 75% of her meals.

Case 2: James, 45, 2-year plateau

Starting point: 92 kg, 178 cm (BMI 29 — overweight), 2 years trying to lose weight with daily cardio without success. TDEE: 2650 kcal. Problem: he ate "healthy" but high in fats (oil, nuts, cheese) without measuring. Target: 2150 kcal + 165 g protein + lower fats to 75 g/day + keep his cardio but add 2 strength sessions. Result at 4 months: 82 kg (-10 kg), +3 kg estimated muscle mass by DEXA. Key: switch from excessive cardio to cardio + strength combination + rigorous fat tracking.

Case 3: Laura, 52, post-menopause

Starting point: 72 kg, 160 cm (BMI 28 — overweight), 18 months after menopause, progressive 8 kg gain over 3 years, irregular sleep. TDEE: 1850 kcal (lower than expected due to hormonal changes). Target: 1500 kcal + 110 g protein + vitamin D and magnesium supplementation + strength work 3 days/week + sleep hygiene. Result at 9 months: 63 kg (-9 kg), significant reported sleep improvement, visibly better body composition. Key: understanding that post-menopause TDEE drops, adjusting expectations, and prioritizing strength over cardio.

How to break a plateau when you've gone 3 weeks without losing

It's inevitable: you will reach a point where the scale stays still for 2-4 weeks in a row even though you keep being disciplined. It's not that your body is "broken" — it's normal metabolic adaptation often combined with creeping caloric underestimation (when you've been dieting a while, portions start growing imperceptibly). These are the four tactics that work according to evidence:

• Weigh and measure everything for 7 consecutive days. Underestimation sneaks in even with veterans. If you've been dieting 3 months, you are probably eating 200-400 kcal more than you think
• Introduce a 1-2 week diet break eating at maintenance. The MATADOR study (Byrne et al., Int J Obes 2018) showed that 2-week periods at maintenance alternated with 2 of deficit produced greater fat loss at 4 months than continuous deficit
• Add 300-500 daily steps before touching calories. NEAT drops unconsciously in a deficit; raising it is more sustainable than cutting more food
• Change macro composition without changing calories. If you've had 3 months of low carbs, raise to 3 g/kg for a week. If you've had months of high carbs, reduce to 2 g/kg. Metabolic variability is sometimes enough of a catalyst

Losing weight with medical conditions: hypothyroidism, PCOS and GLP-1

If you have a diagnosed condition, the principles remain the same — caloric deficit, high protein, strength, sleep — but there are important nuances that your doctor should know and supervise:

Hypothyroidism

With well-adjusted treatment (TSH in range), your TDEE is practically the same as someone without the condition. Without treatment or with insufficient doses, your BMR can be 100-200 kcal lower. Checkup with your endocrinologist at least every 6 months during weight loss: losing fat modifies the absorption and metabolism of levothyroxine and may require dose adjustment. Do not blame hypothyroidism for the absence of loss if you have gone months without bloodwork and without tracking meals.

Polycystic Ovary Syndrome (PCOS)

PCOS runs with insulin resistance in 70-80% of cases according to the Endocrine Society. This makes a diet with moderate glycemic load and lower carb distribution work better for some women — not by magic, but because it reduces the insulin peaks that make fat loss harder. Evidence also supports inositol (myo-inositol 4 g/day) and metformin under medical supervision. Strength exercise is especially important: it improves insulin sensitivity more than cardio.

GLP-1 treatments (semaglutide, liraglutide, tirzepatide)

GLP-1 analogs have transformed the treatment of obesity. Studies like STEP-1 (semaglutide, NEJM 2021) show average losses of 15% of body weight over 68 weeks. But treatment does not replace habits — it enhances them. Patients who combine GLP-1 with high protein (1.6-2.0 g/kg) and strength training lose more fat and less muscle. Without those two pillars, up to 40% of the weight lost can be lean mass, which increases rebound when stopping treatment. If your doctor has prescribed a GLP-1, keep tracking protein and maintain strength work — your final body composition will depend on it.

How to maintain the weight afterwards (the hardest phase)

The science of weight loss is far better known than that of maintenance. Once you reach your goal, the most common mistake is going back to eating as before — and the result is obvious: you regain. What works is the "reverse phase": over 4-6 weeks, increase your calories in 50-100 kcal/week chunks until reaching your new TDEE (which will be lower than the initial one because you now weigh less). This allows your metabolism to adapt gradually, reduces rebound and minimizes rapid fat gain.

The common patterns among those who maintain losses greater than 10% of body weight for 5+ years, according to the National Weight Control Registry (follow-up of 10,000+ people): (1) they eat breakfast almost every day, (2) weigh themselves between 1 and 7 times per week, (3) do at least 1 hour of physical activity daily, (4) watch less than 10 hours of TV per week, (5) maintain a consistent eating pattern between weekdays and weekends. Self-monitoring (tracking meals, regular weigh-ins, activity) is the number one predictor of long-term maintenance. Keep using the tool that got you here — do not abandon it the day you reach your goal.

7-day meal plan (example for 1800 kcal and 140 g of protein)

A concrete weekly plan you can adapt to your tastes is worth more than a hundred theoretical articles. This example is calibrated for a ~65 kg person looking to lose 0.5 kg/week with 1800 kcal, 140 g of protein, 180 g of carbs and 55 g of fats. Scale portions up or down based on your personal TDEE. The five daily blocks include breakfast, mid-morning, lunch, snack and dinner:

Two rules that make this plan flexible in real life: first, you can swap meals between days as long as you keep the order of magnitude (do not swap a 300 kcal salad for a 900 kcal pizza). Second, if one day you go 300 kcal over, do not "compensate" the next day by eating 300 less — just return to your plan. Compensation creates anxiety and restrictive patterns. If you need vegetarian or vegan options, replace chicken/fish/beef with firm tofu (same weight), tempeh (80% weight), seitan (70% weight) or legumes (double weight uncooked). To plan this every Sunday without thinking, read weekly meal prep for beginners with the shopping list and cooking calendar.

Real progress: 6 metrics better than the scale

The scale is a tool — not the only one, and certainly not the most reliable in the short term. Weight fluctuates 1-3 kg per day from water retention, glycogen, salt, hormonal cycle and intestinal contents, without that reflecting changes in body fat. If you measure only weight, you are seeing noise 80% of the time. These 6 metrics give you the real picture of your progress:

• Waist circumference (navel, fasted, weekly). Changes slower than weight but is the best indicator of visceral fat loss according to WHO. Target in women <80 cm, in men <94 cm
• Front + side + back photo every 4 weeks. Same clothes, same light, same time of day. Changes are better seen in visual comparison than on the scale
• How your base clothes fit. Pick 2 items (pants + fitted shirt) that now fit tightly. Try them on every 3 weeks. When you notice looseness, you have lost fat even if the scale does not move
• Strength in 3 base exercises: squat, bench press (or push-ups) and deadlift (or row). Record weight x reps every 2 weeks. If you raise strength while losing fat, you are doing body recomposition — the ideal scenario
• Subjective energy and rest (1-10 scale on waking). If you drop your calories too aggressively, energy falls first. It is the earliest sign that you need a diet break or to raise by 100-150 kcal
• Adherence to the 5 core habits: log >80% of meals, 3 strength sessions, 7+ hours sleep, 8,000+ steps, 1.6-2.2 g/kg protein. If all 5 are green for 4 weeks in a row and you do not lose weight, then we touch calories

The scale is still useful when you use it well: weigh yourself 3-7 times per week fasted after urinating, and average the values of the last 7 days. That weekly average is your real number. There are apps that calculate it automatically (Renzy, Happy Scale) and save you the psychological stress of daily ups and downs. If you see two consecutive weeks with the weekly average equal or rising, it is time to review — not before.

Renzy vs MyFitnessPal vs Yazio vs Lifesum: honest 2026 comparison

Choosing the app that will accompany you for 6-12 months is an important decision — adherence depends 40% on how comfortable it feels according to Burke et al. (J Acad Nutr Diet 2011). This is an unvarnished comparison of the 4 most popular apps for weight loss in 2026, based on their public versions as of this guide:

The honest conclusion: if you value minimal friction above all when logging (3 seconds per meal via photo), Renzy is your tool. If you prioritize a huge community and do not mind ads, MyFitnessPal covers the basics. If you want a low price with visual recipes, Yazio works. No app "does the diet for you" — they are all instruments. The best one is the one you open tomorrow, and the day after, and in three months without quitting.

Glossary: 14 terms you will hear in any serious article about losing weight

So you can read any study or article without getting lost, here is the essential vocabulary with concise scientific definitions:

• TDEE (Total Daily Energy Expenditure): total calories you expend in a day. It is the sum of BMR + TEF + EAT + NEAT. Your "maintenance"
• BMR (Basal Metabolic Rate): calories you would burn if you were lying still for 24 hours. Represents 60-70% of your TDEE
• TEF (Thermic Effect of Food): calories your body spends digesting what you eat. Protein: 20-30%, carbs: 5-10%, fat: 0-3%
• NEAT (Non-Exercise Activity Thermogenesis): calories burned from non-exercise movement — walking, fidgeting, typing, climbing stairs. Varies up to 800 kcal/day between people
• EAT (Exercise Activity Thermogenesis): calories spent on structured sport sessions. Usually only 5-15% of total TDEE
• Caloric deficit: eating less than your TDEE. Necessary to lose fat. Recommended 300-500 kcal or 20-25% below TDEE
• Metabolic adaptation: reduction of BMR and NEAT after prolonged weight loss. Makes losing progressively slower
• Body recomposition: losing fat and gaining muscle simultaneously. Possible in beginners, overweight and after a long layoff
• MPS (Muscle Protein Synthesis): muscle protein synthesis. Stimulated by eating 25-40 g of protein per serving with ~2.5 g of leucine
• GLP-1 (Glucagon-Like Peptide-1): intestinal hormone that regulates appetite and satiety. Synthetic analogs (semaglutide) are anti-obesity drugs
• Ghrelin: hunger hormone. Rises before eating and falls after. Sleep deprivation raises it chronically
• Leptin: satiety hormone produced by adipose tissue. Drops during caloric deficit, which is why you feel hungrier after losing weight
• Glycemic index (GI): the speed at which a food raises blood glucose. Relevant in diabetics; secondary in the general population when total calories are controlled
• Recomp / Refeed / Diet break: deficit management strategies. Refeed = 1-2 days at maintenance; diet break = 1-2 weeks at maintenance. Both reduce metabolic adaptation

How Renzy automates the whole process

Everything above — calculating TDEE, setting a deficit, monitoring protein, logging meals, detecting underestimation, adjusting based on results — can be done manually with a spreadsheet and a lot of patience. Or you can let AI do the heavy lifting while you decide what to eat. Renzy uses computer vision to identify foods in a photo in 3 seconds, calculate calories and macros with a 10-15% margin of error (comparable to a human nutritionist according to a 2024 MIT study), and automatically adjust your TDEE as you lose weight using regression algorithms over your real trend (not the theoretical one). If you want to understand the vision behind the product, artificial intelligence and the future of nutrition explains where this technology is headed.

Creating an account is free and requires no credit card. You get basic scanning included, the trends dashboard, automatic TDEE/deficit calculation and personalized recommendations by goal (lose fat, gain muscle, maintain). If at some point you want full access — unlimited scanning, micronutrient analysis, AI weekly planner, reports for your nutritionist — you can upgrade to Pro for €19.99 per month. But it is not mandatory: the free plan covers 80% of what you need to lose weight consistently for the next 6 months.

Conclusion: sustainable weight loss is a system, not a diet

If you take away a single idea from this guide, let it be this: losing weight is not an event that starts and ends — it is a system you maintain. Named diets (keto, fasting, paleo, Dukan, Mediterranean) work or fail based on how well they help you maintain a sustainable caloric deficit with enough protein, sleep, activity and stress management. There is no magic food, no critical time of day, no forbidden macro. There is basic science, long-term adherence, and tools that reduce daily friction. The rest is marketing noise.

Start today with three concrete things: (1) calculate your TDEE with Mifflin-St Jeor and set a 400 kcal deficit; (2) write down on paper the 4 protein sources you are going to rotate this week; (3) decide at what time you are going to sleep for the next 30 days and protect that commitment as if it were a work meeting. Repeat the process for 12 weeks, measuring the weekly trend. At that point you will know if your plan works, and you will have enough data to adjust it. This, and no other diet, is the formula with the most scientific evidence and real long-term success cases.