Lose fat, even on busy days

1. The science, briefly

Body fat goes down when, over a period of weeks, you take in less energy from food and drink than your body uses. The gap is called a calorie deficit. Your body covers the shortfall from its own stores.^[1] Eat enough protein and do some strength training, and more of what it draws on is fat rather than muscle.^[2]

A few things are worth knowing, because they are where people lose heart:

• No single food or trick changes the sum. Not a supplement, a meal time or a "fat-burning" food. Even protein, the costliest food to digest, uses up only a fraction of the energy it brings in.^[3]
• The scale moves with water. Day to day, your weight goes up and down mostly with water, stored carbohydrate and food you haven't digested yet. Each gram of stored carbohydrate (glycogen) is held with about 3 g of water.^[4] Judge progress by the trend over two to four weeks, not one reading.
• The first week flatters you. Start eating a little less and the first week or two often shows a big drop. Much of it is water leaving with stored carbohydrate, so expect the pace to settle after that.^[4][5]
• Slow and steady keeps muscle. A pace often recommended for keeping muscle while you lose fat is around 0.5 to 1% of body weight a week.^[6][7] Strathlon stays at the gentler end of that: it works out a pace from your goal weight and plan length, and never sets it faster than about 0.65% of your body weight a week. If you haven't set a goal weight, it uses a small, fixed daily cut instead.
• Protein and lifting protect muscle. Strathlon gives you a daily protein target: for Fat Loss it is 2.2 g per kg of body weight, worked out from a healthier reference weight if you have a lot to lose. That sits within the range research supports for keeping muscle in a deficit.^[8][2]

2. What gets in the way

For most people the rule isn't the problem. Keeping to it every day is.^[9] And on a busy day, logging food is usually the first habit to go. Finding the right entry in a long list, guessing a portion, remembering the biscuit at four o'clock: each one takes a minute you don't have.

There is a second, quieter problem. Most people record less than they eat. Across five large studies that checked people's food records against lab measurements, energy intake was under-reported by about 15 to 30% on average.^[10] It tends to happen when logging is slow and memory fills the gaps. A gap that size can cancel out a sensible deficit on its own.

3. How Strathlon takes the chore away

The aim is simple: make each meal quick to log, so it still gets logged on the days you are short of time. Most of it starts on the AI Coach tab.

• Food from a pack. Take a photo of the pack with its barcode showing. Strathlon reads the barcode from the photo and fills in the pack's own figures from Open Food Facts, a free public database of food labels. The card is headed Food detected — pack figures, and you then say how much you had. There is no separate scanner to find.
• No match? Three buttons appear under the card. Photograph the label reads the printed nutrition panel instead; Describe it and Another photo are the other two routes.
• A meal on a plate. Photograph it, add a few words if you like, and tap Analyse Photo. Or skip the photo and type what you ate, such as "chicken curry with rice". Either way you get an estimate of the calories, protein, carbs and fat. It is an estimate, and a short description alongside a photo makes it closer.
• You didn't finish it. Tap I didn't finish this, then describe or photograph what's left. The coach works out what you actually ate. If the meal is already on your Tracker, you can update that entry rather than adding a second one.
• A running total. Each meal you add with Add to Tracker lands on the Tracker, so you can see what you've eaten so far against your target for the day.

Photo logging, barcode and label reading, describing a meal to the coach and the leftovers fix are part of the AI Coach subscription. Without it you can still type your day's calories into the Tracker yourself.

4. Use your numbers to decide

The top of the Tracker shows four figures: your Target for the day, what you've Burned, what you've Consumed, and the gap between burned and eaten, which reads Deficit for Fat Loss. A look before dinner tells you how much room is left, while there is still time to use it.

Had more than you planned? You don't have to write the day off. Go for a walk, or do any other activity, then log it: on the Plan tab, tap Add activity, choose it and say how long it lasted. Your target for the day rises by the app's estimate for that activity, so you can see exactly how much room it made.

• For a brisk 30-minute walk, the app's estimate is about 130 kcal for someone weighing 80 kg. It scales with your weight, so it is a little less if you're lighter and more if you're heavier. If you enter the distance, it works from that instead.
• The app counts only the extra energy the activity used on top of an ordinary day, so its figure is lower than the total some watches show.
• An activity you log is counted in full on that day. Sessions already on your plan are counted for you, so Add activity is for anything extra.
• Activity figures are estimates. Log only what you actually did, and let your weight trend over a few weeks tell you whether the numbers are working for you.

For that trend, open Progress. The Body weight chart plots your weigh-ins against a line predicted from the calories you've logged, and its trend line smooths out the daily water swings.

5. Your sport, and where to read more

If you play a sport and picked Sports Performance as your second goal, your plan keeps the same steady deficit and adds back what each sport session uses on the days you play or train, with more carbohydrate on those days. Your gym sessions also include moves picked for your sport.

If you have periods, your weight often sits a little higher around your period because of water, not fat.^[11] There is more in nutrition across your cycle.

Want the detail? These go deeper:

• Fat loss fundamentals: deficit size, plateaus and a worked example
• Diet breaks and refeeds
• Fitness myths, corrected
• Fuelling guides for every sport and strength guides for every sport

6. Staying safe

• Strathlon keeps your pace to about 0.65% of your body weight a week at most, and it never sets a daily target below a minimum: 1,200 kcal for women and 1,500 kcal for men, or what your body burns at rest if that is higher.
• Under 18? Fat Loss isn't offered, and the app never sets a calorie deficit.
• Pregnant or breastfeeding? The app sets no calorie target at all and asks you to follow your midwife's or doctor's guidance on eating.
• If your answers to the food questions in setup suggest care is needed, the app keeps your calories at maintenance, stops showing tips about eating more or less, and asks the coach to keep the focus off calorie counting.

None of this replaces medical advice. If you have a health condition or a history of disordered eating, or you're unsure whether a plan is safe for you, speak to your GP or a registered dietitian first.

References

The figures in this guide come from the sources below. Where a number reflects a professional body's guidance, the citation names that body and its country. Facts about how Strathlon works come from the app itself.

1. Hall KD, Heymsfield SB, Kemnitz JW, Klein S, Schoeller DA, Speakman JR. Energy balance and its components: implications for body weight regulation. American Journal of Clinical Nutrition. 2012;95(4):989–994. Sets out the energy-balance framework for body-weight change. PMC3302369
2. Trexler ET, Smith-Ryan AE, Norton LE. Metabolic adaptation to weight loss: implications for the athlete. Journal of the International Society of Sports Nutrition. 2014;11:7. States that structured resistance training and sufficient protein preserve lean body mass during energy restriction. PMC3943438
3. Westerterp KR. Diet induced thermogenesis. Nutrition & Metabolism. 2004;1:5. Gives the energy cost of processing each nutrient (20–30% for protein, less for carbohydrate and fat), always a fraction of the food's energy. PMC524030
4. Fernández-Elías VE, Ortega JF, Nelson RK, Mora-Rodriguez R. Relationship between muscle water and glycogen recovery after prolonged exercise in the heat in humans. European Journal of Applied Physiology. 2015;115(9):1919–1926. Each gram of glycogen is stored in muscle with at least 3 g of water. PubMed 25911631
5. Kreitzman SN, Coxon AY, Szaz KF. Glycogen storage: illusions of easy weight loss, excessive weight regain, and distortions in estimates of body composition. American Journal of Clinical Nutrition. 1992;56(1 Suppl):292S–293S. Glycogen is stored with three to four parts water, so early weight loss on a very-low-calorie diet largely reflects glycogen and its water. PubMed 1615908
6. Helms ER, Aragon AA, Fitschen PJ. Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation. Journal of the International Society of Sports Nutrition. 2014;11:20. Recommends weight loss of about 0.5–1% of body weight a week to maximise muscle retention. PMC4033492
7. Aragon AA, Schoenfeld BJ, Wildman R, et al. International Society of Sports Nutrition (ISSN, United States) position stand: diets and body composition. Journal of the International Society of Sports Nutrition. 2017;14:16. Repeats the 0.5–1.0% a week rate and notes slower loss better preserves lean mass. PMC5470183
8. Morton RW, Murphy KT, McKellar SR, et al. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. British Journal of Sports Medicine. 2018;52(6):376–384. No further gains beyond about 1.6 g/kg/day, with the upper confidence limit at about 2.2 g/kg. PubMed 28698222
9. Thomas DM, Martin CK, Redman LM, et al. Effect of dietary adherence on the body weight plateau: a mathematical model incorporating intermittent compliance with energy intake prescription. American Journal of Clinical Nutrition. 2014;100(3):787–795. Concludes that lapses in adherence are a major contributor to the weight-loss plateau. PMC4135489
10. Freedman LS, Commins JM, Moler JE, et al. Pooled results from 5 validation studies of dietary self-report instruments using recovery biomarkers for energy and protein intake. American Journal of Epidemiology. 2014;180(2):172–188. Average under-reporting of energy intake of about 28% (food-frequency questionnaire) and 15% (24-hour recall). PubMed 24918187
11. Kanellakis S, Skoufas E, Simitsopoulou E, et al. Changes in body weight and body composition during the menstrual cycle. American Journal of Human Biology. 2023;35(11):e23951. Body weight was about 0.45 kg higher during menstruation, attributable to extracellular water. PubMed 37395124

This is general educational information rather than medical, dietary or coaching advice. Figures are population-level guides from published research, and individual results vary. Anyone with a health condition, a history of disordered eating, or who is pregnant or postpartum should consult a qualified physician or registered dietitian before starting or changing an exercise or nutrition programme. See our Terms for more.

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