You come back from your run, your watch reports an impressive calorie number, and the fridge door is already open. What happens in the next ten minutes decides whether this workout moves you forward with fat loss or just makes you hungry. This article is about exactly those ten minutes, and about everything that comes before and after.
I'm a personal trainer and a former chef, and I build plans with runners and strength athletes. My stance on losing weight alongside training fits in one sentence: whether and how far someone goes into a deficit, I decide by the training phase and not by the calendar. The deficit is built so that the important sessions stay fuelled and the muscle stays. The goal is less body fat at the same performance, not the fastest number on the scale.
Check the phase first, then the deficit
Two sentences lead you astray when you want to lose weight. One goes: "I train so much already." The other: "Then I'll just eat less." The first overestimates what training burns. The second underestimates what training needs.
That's why I ask four questions before any deficit. Is this a calm phase, meaning base or strength block? Is your weight stable, or rising without a plan? Do sleep, mood and performance look fine? Is there a reason that really matters to you, and a time window for it? Four times yes, and you may plan.
The answer depends on the phase. In the build-up to a race a deficit doesn't belong on the list, and if your weight falls unintentionally, the answer is eat more, not less (IOC consensus on relative energy deficiency, Mountjoy et al., 2023). In the first weeks after a marathon, recovery comes first, and I don't cut hard there. Calm base or strength blocks fit. Winter is a possible window, but not an automatic one. To be honest about it: this phase logic is derived coaching practice. Nobody has tested it in recreational athletes.
And yes, in the article on eating when you train a lot the advice was: eat enough, your appetite isn't a reliable gauge. This one is about a deficit. Both are true, just in different phases and for different goals. If you're preparing for races and want performance, you need energy. If you're in a calm phase and want to lose body fat, you need a deficit that is time-limited, moderate and monitored.
How big can the deficit be?
There is no single number for everyone. Someone tall with more body fat tolerates more than someone small and lean (Hall et al., 2011; Heymsfield et al., 2014). That's why I don't calculate in calories, I calculate in your body weight. The best yardstick is roughly half a percent to one percent of your body weight per week, and if you're aiming for performance, stay toward the lower end (ISSN position stand, Aragon et al., 2026; Helms et al., 2014; Garthe et al., 2011). The data behind it is thin, but it's the most reliable guidance we have.
| Body weight | 0.5 % per week | 1 % per week |
|---|---|---|
| 60 kg | 300 g | 600 g |
| 70 kg | 350 g | 700 g |
| 80 kg | 400 g | 800 g |
| 90 kg | 450 g | 900 g |
This is arithmetic, not a study value. As a rough rule of thumb for performance-oriented people with light to moderate body weight, about 300 to 500 calories below your expenditure fits. That, too, is a ballpark figure: the number circulates in the press without a source, and at 90 or 100 kilos it works out to be lower. Garthe and colleagues saw in 24 elite athletes that a slower pace tended to hold strength and performance, and how far that transfers to recreational sport is limited.
Your test is your week: if the hard sessions get worse, the deficit is too big, and you take it back.
Because it belongs here: my book "Minus 10 in 60 Tagen" (in German) calculates bigger. That is a limited 60-day window in which weight loss comes first and performance may suffer temporarily. This article is about the opposite, losing weight while holding performance, which is why the deficit is smaller. Both paths are honest, they just have different goals.
After the race: less volume, same hunger
If your weight goes up after a race, in the first week or two it's often water and refilled stores at first: your body puts carbohydrates back in and binds water with them (Kreitzman et al., 1992). That is recovery, not failure, and nothing gets cut there.
The real trap comes afterwards. You run less, but hunger and portions keep running at in-season level. If you burn less and eat the same, there's something left over at the end. That is logic, not a measurement, because there are no studies on runners after the end of the season. Observations over years show that people who run less long-term tend to gain weight on average (Williams & Thompson, 2006). Whether and when appetite adapts, nobody knows exactly.
My way: bring food and volume down together. For the first week or two you cut nothing, then the extras go first: bars, snacks after the run and liquid energy. The drink from the fuel article gets left out then. The main meals stay. Then you look at the weekly average, not at the morning after. I won't give you a kilo number that would be "normal", because there's no reliable basis for one.
Running alone doesn't make you lean, and your watch is unreliable
Running stays great for your heart, your head and your endurance. For weight loss it often works less than expected (Jayedi et al., 2024; Thorogood et al., 2011), because part of the expenditure gets lost again: through more hunger, through the reward meal afterwards, through less movement in the rest of the day. How much differs from person to person (Flack et al., 2020; King et al., 2008). An example: an hour of running looks like a mountain on the watch, and one bar plus an evening on the sofa carry it right back.
And the watch? Its calorie number is a rough estimate. The errors go in both directions depending on brand and activity, and none of the devices tested came in under 20 percent error (Shcherbina et al., 2017; Fuller et al., 2020). So don't eat it back. What I advise runners who run a lot and don't lose weight: a fixed meal after the run instead of "I earned this", keep an eye on your steps in everyday life, and measure by the weekly average. For me, steps in everyday life rose a lot in 2023: one to two hours of walking in the evening, roughly 20,000 a day by my estimate, compared with 5,000 to 7,000 before. That's my memory, not a log.
Where you cut, and where you never do
You take the deficit from calm days and from the extras, not before the long run and not before heavy strength work. One to three sessions a week are the ones that matter, and you fuel those fully. Eating before long or hard endurance sessions helps performance (Aird et al., 2018). My breakfast when performance is on the line: yoghurt with granola or oats and honey, carbohydrates plus protein, because the energy has to get into your running shoes and onto the mat fast.
Running fasted brings no advantage for fat loss when the deficit is the same (Schoenfeld et al., 2014, small study). So you don't have to torture yourself. The weekly split itself, fuelling key sessions fully and keeping calm days smaller, is coaching practice with no direct comparison study. It does fit what we know about energy and performance.
Muscle in a deficit: heavy weights, protein spread out
The stimulus that tells your body "keep the muscle" is heavy lifting. My framework in a deficit: two strength sessions a week, main lifts heavy, just like before. If time gets short or you're tired, you cut sets, not weight. Add roughly 1.6 to 2.2 grams of protein per kilo of body weight, spread across several meals (Aragon et al., 2026), which is around 110 to 150 grams at 70 kilos. With kidney disease, clear the amount with your doctor first.
Two caveats belong here. Protein doesn't rescue a deficit that is too big: at about 500 calories of deficit, one analysis found no muscle gain any more (Murphy & Koehler, 2022), and in young women at an energy availability of about 25 kcal per kg of fat-free mass, muscle protein synthesis and lean mass fell (Oxfeldt et al., 2023). One exception: young men under controlled conditions gained muscle for four weeks despite a 40 percent deficit on very high protein (Longland et al., 2016), which is not recreational everyday life. In a deficit, keeping muscle is the goal, not building it. Sleep counts too (Nedeltcheva et al., 2010, small study).
My own contrast: my first month in 2023 was just "eat less", with no strength stimulus and no protein knowledge, with hunger attacks, and I suspect I lost muscle. That's exactly what I want to spare you.
The plate in a deficit
What fills you up is mainly protein and lots of vegetables (Manore, 2015), because vegetables bring volume for little energy (Robinson et al., 2022). On calm days half the plate is vegetables, plus chicken, fish, tofu or two to three eggs, a little rice, a sauce that tastes good. Before a hard session you flip it around: more rice or pasta, less raw vegetables, which only fill you up. Oil doesn't have to go, measuring it once is enough. As a chef I know what a drop of oil in the pan can do, and a spoon instead of a splash is a difference you can't see on the plate. At least three meals a day with protein.
And set meals instead of eating on the side. In my time as a chef I had no breakfast in the morning, two or three coffees, and then all day something on the side, standing and walking. I counted nothing. In 2023 I cut the eating on the side and ate set meals, for example chicken with rice and sauce, or fried vegetables with meat or fried eggs. That is my memory. And to be honest: I never did meal prep back then, today I recommend it to every client.
When the scale stands still
Your weight fluctuates daily through water, carbohydrates, day of the week and, for women, the cycle (Orsama et al., 2014; Kreitzman et al., 1992), and with new strength sessions the muscles can hold extra water. A single morning says little, a two-week average says more.
My order before I cut further: first the two-week average instead of the daily value (weigh several times a week and take the mean). Second, write down honestly what you eat, including the bits on the side. Third, check your steps in everyday life. Only when all of that fits and the average hasn't dropped for two weeks are there two paths: a diet break of about a week at maintenance, or a very small step down. A diet break doesn't make you lose weight faster, but it can ease hunger and mood (Peos et al., 2021; Poon et al., 2025), and the evidence is mixed: an earlier study in men with obesity saw an advantage only in a per-protocol analysis (Byrne et al., 2018). I myself ate at maintenance calories for about two weeks near the end of 2023 when I hit a plateau, then carried on. That's experience, not proof.
When the deficit ends immediately
This is the most important section, and it's not fear mode, it's a safety line.
See a doctor immediately and stop the deficit: chest pain, heart racing or palpitations, shortness of breath, fainting or severe dizziness during exercise. For acute chest pain or fainting, call 112 (the German emergency number). The same applies to a stress fracture or bone pain, and if a woman's period stops or becomes clearly irregular (Williams et al., 2026; Gordon et al., 2017). The pill can mask bleeding, so watch the other signs. From 40, a change can also have other causes: get it checked, don't interpret it yourself.
Plus medical and psychotherapeutic help: persistent thoughts about food, fear of eating, binge eating, vomiting, compulsive exercise, depressed mood (Wells et al., 2020).
Pause the deficit, eat at maintenance for one to two weeks and observe, otherwise get it checked: performance drops over two weeks, sleep gets poor, constant tiredness, frequent infections, reduced libido, or your weight falls faster than planned. The two-week mark is a coaching convention, not a study threshold. One more note: if you have a history of an eating disorder, are pregnant, breastfeeding or have a medical condition, don't plan a deficit on your own. Alethics doesn't diagnose.
Your four-week check
A deficit needs an end at which you evaluate. Before the start you check the phase, set the deficit and protect the important sessions. Every week you weigh yourself several times under the same conditions and note the weekly average, your strength numbers on the main lifts, and a feel from 1 to 5 for your important sessions. After four weeks you compare the average of week 1 with week 4 (Aragon et al., 2026), not a single morning. Then there are four answers: carry on as before, a smaller deficit, a pause, or stop. The four-week rhythm is practice and not a validated protocol.
What helped me most in 2023 was finding a system that fits into everyday life, plus enough sleep and good food. If you have no plan, the plan starts without you, so the routine is free to print: comment DEFIZIT under one of my Reels or carousels on Instagram or send me the word as a DM (the guide is in German), and you'll get the Four-Week Check with the calculation, weekly log and stop signals.
This article does not replace medical advice. Alethics does not diagnose. All frameworks, doses and rules of thumb are coaching practice, not study results; the studies mostly come from small, often young or highly trained groups.
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Keep reading
- Under-eating despite training
- The winter block after a marathon
- Compound lifts for strength and endurance
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