What to Eat to Lose Weight and Body Fat

"Calories in, calories out." It's the fundamental equation determining "energy balance," which governs your body weight. Or is it?

The physics behind the energy balance equation is solid, but the application of it is not as straightforward — and even if you get the maths right, what those calories are made of changes how easy or hard the whole weight loss process feels.

Energy balance: The maths

At its core, body weight change follows the first law of thermodynamics: "energy cannot be created or destroyed, only transferred or transformed". When energy intake exceeds energy expenditure, the excess is stored, primarily as fat tissue.

But when expenditure exceeds intake, stored energy is mobilised to meet the deficit — mainly from fat, but also from carbohydrate and protein stores in the liver and muscles.^[1]

Energy intake and expenditure are usually measured in "calories," which are actually kilocalories (1,000 calories = 1 kilocalorie).

Your body (like everything else) follows the laws of physics, making energy balance the ultimate determinant of successful fat loss. However, the apparent simplicity of this equation masks a lot of complexity in both measuring it and adjusting its individual parts to "create" a calorie deficit.

In our opinion, you're better off focusing on doing things that lead to a negative energy balance, rather than obsessing over energy balance itself.

Calories in: Why tracking is harder than it looks

Energy intake is easy to measure, but difficult to measure correctly. You can have the most detailed, sophisticated tracking system in the world, and it still won't measure what your body is actually absorbing. Food-logging studies generally show underreporting of energy intake by 10–20%, though some people underreport by 40% or more. This comes down to:^[2]

• Misjudging portion sizes.
• Failing to account for calorie-dense additions (cooking oils, spreads, condiments).
• Different cooking or processing methods.
• Selective counting (ignoring weekends or eating out) and relying on flawed food databases.
• Restaurant and pre-packaged food labels are notoriously inaccurate, and liquid calories (e.g., milk, alcohol, sodas, and sauces) are frequently overlooked entirely.

Add up all these errors, and you're really left asking: how good is your educated guess? Trying to get it to the nearest 100 calories — no chance.

Calories out: Your total daily energy expenditure

The other side of the equation is your total daily energy expenditure, and it has four components:

1. Basal Metabolic Rate: The energy required for your basic biological needs. Accounts for roughly 60–75% of your energy expenditure for most people.
2. Thermic Effect of Food: The energy required to digest, absorb, and use the energy you've eaten — usually 8–12% of energy expenditure.
3. Exercise Activity Thermogenesis: all planned exercise. Typically, 5–15% of energy expenditure, but can exceed 50% for very active people and drop under 5% for inactive ones.
4. Non-Exercise Activity Thermogenesis: all other movement that isn't sleeping, eating, or exercising — fidgeting, posture, incidental activity. It varies enormously between people (think farmworker versus desk worker) and is a crucial, often-overlooked component of energy balance.^[3]

All four components fluctuate day to day and hour to hour, which makes assumptions about how much energy they use genuinely difficult. Exercise is relatively easy to track — minutes, sessions, distance. But when you reduce how much you're eating, your body also reduces how much it expends. This is called "metabolic adaptation" or "adaptive thermogenesis."

Your basal metabolic rate drops as your organs become more energy-efficient, and you subconsciously reduce your non-exercise energy expenditure too, resting more and moving less. These compensatory behaviours can add up to hundreds of calories a day. Your body isn't trying to sabotage your diet; these are evolutionary survival mechanisms that kept us alive through famines.^[4]

Why Most Diets Fail

Despite the unwavering certainty of the underlying physics, relying on calorie counting alone runs into three pitfalls.

1. First, increasing your energy expenditure increases your appetite and drives you to seek out tasty, energy-dense foods.
2. Second, you probably can't measure your energy intake accurately enough to make small, meaningful reductions.
3. Third, you probably can't measure your daily energy expenditure accurately enough to hit a meaningful energy balance target.

Add in the large variation between people in all of these components, and it's no surprise your energy balance estimates rarely translate to what you see on the scale, no matter how hard you try. A more sophisticated, nuanced approach is required.

Protein: The quadruple advantage

Protein is a powerful but overlooked macronutrient to support fat loss, working through four distinct mechanisms.

1. Satiety: High-protein meals produce 25–50% greater fullness ratings than high-carb meals of equal calories. Protein stimulates appetite-suppressing gut hormones (e.g., GLP-1, PYY, CCK) while reducing "hunger hormone" ghrelin. These effects can begin within minutes of eating protein and last for hours.^[5]
2. Thermogenesis: Digesting protein burns more energy, 20–30% of its calories, compared to 5–10% for carbohydrates and under 3% for fat. So of every 100 calories of protein you eat, only 70–80 calories are actually available for use once digestion is accounted for.^[6]
3. Muscle: High protein intake helps preserve and potentially build muscle when combined with resistance training, which in turn burns extra calories. People consuming higher protein while losing weight maintain substantially more muscle than those following standard protein recommendations.^[7]
4. Reduced intake: Protein-rich meals naturally lead to eating less food overall. High protein intake can reduce total calorie intake by 200–500 calories a day without any deliberate restriction, willpower, or portion control.^[5][6]

How much protein do you actually need?

The "optimal" amount depends on your activity level, fat loss goals, and personal preferences. To lose fat while maximising muscle retention, you should aim for 1.6–2.4 grams per kilogram of body mass a day while restricting calories. For a 100 kg person, that's 160–240 grams a day, split into 40–60 gram servings across three to five meals.^[8]

The upper end of this range (above 2.0 g/kg/day) is for people with more muscle, higher activity levels, a goal of gaining (not just maintaining) muscle, or running a larger calorie deficit.

Older adults and those with metabolic disorders may also benefit from higher intakes, since older muscle needs proportionally more protein to trigger the same growth response. However, for everyone else, wanting to lose body fat can aim towards the lower end (i.e., 1.6 g/kg/day). There's little evidence that eating more than this amount has further benefits.^[9]

During calorie restriction, your body is more likely to break down both fat and muscle for energy — eating adequate protein shifts that balance toward burning fat. This matters because muscle burns two to three times the energy of the same amount of fat tissue, so maintaining (or building) muscle tends to produce greater, more sustainable fat loss. This is also why resistance training is advised alongside any fat-loss diet.

What type of protein matters for fat loss

Not all protein sources are equal. "Complete proteins" (i.e., containing all nine essential amino acids in adequate amounts) offer superior muscle-building, health, and satiety benefits. The amino acid leucine plays a particularly important role in stimulating muscle growth and fat burning.

Animal sources (e.g, lean meats, poultry, fish, eggs, dairy) are naturally complete and typically provide the most leucine per serving. Plant proteins can support fat loss too, but often need combining to achieve a complete amino acid profile — legumes, quinoa, soy, nuts, and seeds are good high-quality options, alongside more everyday sources like wheat, rice, and corn. Plant proteins also bring fibre and phytonutrients and tend to be lower in calorie density, which can make them a better option in most cases.

Why food quality matters

All calories provide energy, but their effects on hunger, your hormones, and long-term health prospects vary dramatically depending on the food source. "Nutrient-dense" foods are rich in vitamins, minerals, fibre, and other beneficial compounds (antioxidants, prebiotics) relative to their calorie content, and they work with your body's natural hunger and satiety signals.^[10]

Low-quality calories from highly processed foods, by contrast, often lack these nutrients while promoting overconsumption through poor satiety signals and rapid absorption. Even if the macronutrients, sugar, sodium, and fibre are the same, people eat around 500 calories a day more when eating freely from an ultra-processed diet versus a whole-food one.^[11]

Processing removes or alters the natural "matrix" of nutrients that supports appetite regulation. So, whole foods take more energy to digest and release nutrients more gradually, which keeps hunger at bay for longer.

Pairing protein with fibre

The most satiating calories combine protein and fibre, which work together through different mechanisms: protein triggers appetite-suppressing hormones and burns energy to digest, while fibre adds bulk, slows digestion, feeds your gut bacteria, and produces its own feelings of fullness.^[12]

Pairing both legumes or lean meat with vegetables maximises fullness per bite, naturally extending the time between meals and reducing daily intake without any extra restriction or willpower required.

Nutrient density, food volume, and blood sugar

Micronutrients also play a role. B vitamins, calcium, copper, iodine, magnesium, and iron support efficient calorie-burning and energy expenditure, while antioxidants from colourful fruits and vegetables (e.g., carotenoids, flavonoids, polyphenols) can reduce inflammation and support appetite regulation.

On a restricted diet, each calorie needs to work harder to deliver these nutrients, so nutrient-dense choices matter even more. There's limited evidence that micronutrient deficiencies directly drive overeating, but they do support energy levels, mood, and cognitive function — all of which can indirectly affect adherence to your programme.

Low-energy-density foods let you eat larger, more satisfying portions for fewer total calories, making a deficit feel less restrictive. This "volumetrics" principle leverages your stomach's stretch sensors, which signal fullness to your brain.^[13]

Fruits and vegetables are typically 80–95% water plus fibre, offering real volume for minimal calories. A 200 g salad might contain 50–75 calories, versus 600–800 calories for the same weight of a doughnut.

Whole grains, legumes, and lean proteins sit in between: moderate energy density, high nutrient value, and better satiety than processed foods. Larger portions also create a psychological "I'm full" cue that complements the physiological signals.

Excessive refined carbs and added sugars cause rapid blood glucose and insulin spikes and crashes, which trigger the return of hunger and cravings — a cycle of eating, dissatisfaction, and more eating that also encourages fat storage and dampens fat-burning.^[14]

Eating protein- and fibre-rich whole foods instead promotes more stable blood sugar levels, sustained energy, and hormonal patterns that support fat burning over storage.

Healthy fats (nuts, seeds, avocado, olive oil) shouldn't be overlooked either. They support vitamin absorption, provide energy without spiking glucose or insulin, and supply the essential fats your cells and hormones need.

Practical applications

Use calorie counting as a tool, not a target

Fat loss isn't just physics. It requires a basic understanding of biology and psychology as well. Calorie counting has its place: it's useful for building awareness of habits, monitoring progress, portioning and planning meals, and making informed food choices.

It's far less useful as a precise tool for hitting specific weight or fat-loss targets, and it tells you nothing about health. Eating 2,000 calories of junk food every day will not lead to the same health outcomes as eating 2,000 calories of whole foods a day.

Build your protein habit gradually

Rather than overhauling everything in your diet all at once, increase protein intake by 10–20 grams a day, or every other day, until you reach your protein target.

Batch-cook proteins like grilled chicken, hard-boiled eggs, or legume-based spreads to remove daily decision-making, and keep convenient options on hand for unpredictable days (e.g., canned fish, protein powders, Greek yoghurt, pre-cooked lean meats).

Cost-effective staples like eggs, canned fish, dried legumes, and milk protein powder (bought in bulk and frozen where possible) keep it sustainable.

Upgrade your calorie quality gradually

Don't aim for perfection, total elimination, or crash diets. Instead, go for gradual shifts with room for flexibility.

• Prioritise protein and fibre first (vegetables, whole grains, legumes, fish, dairy, lean meats), then layer in healthy fats.
• Make simple swaps that keep familiar flavours: steel-cut oats over instant, whole fruit over juice, grilled chicken over processed lunch meat, whole-grain bread over refined.
• Even treat foods can be paired with something nutrient-dense (milk and cookies, peanut butter and apple slices).
• Make the healthy option the easy option by pre-cutting, pre-cooking, and pre-portioning it.
• Apply a simple "one ingredient rule" when shopping — if there's an ingredient list, can you recognise everything on it?
• Optimise the foods you already eat most often first, and avoid changes you can't realistically sustain given your social, financial, or practical constraints.

Bottom Line

Fat loss ultimately comes down to energy balance — but treating it as a maths problem misses most of what actually determines success. Both sides of the energy balance (i.e., calories in and calories out) equation are harder to measure than they look. And your body actively adapts to resist the deficit you're trying to create anyway.

Protein and food quality are what make the equation workable in practice: protein preserves your muscle and keeps your appetite under control, keeping an energy deficit sustainable. Nutrient-dense, high-fibre, lower-energy-density foods work with your biology instead of against it.

The best approach isn't the one with the most precise numbers — it's the one that combines a sensible deficit with the food quality and habits you can actually stick to.