Dr Nick Fuller
Leading Obesity Expert at the University of Sydney and founder of Interval Weight Loss.
You’re doing all the ‘right’ things—swapping chips for carrot sticks, cutting back on sugar, loading up on salads—and yet, the scales keep creeping up. Frustrating, right?
Here’s the deal: healthy eating doesn’t always equal weight loss. And no, it’s not your imagination. For instance, according to a 2017 review, cutting calories alone often backfires. Your body can respond by slowing your metabolism and ramping up your hunger, making long-term weight loss harder, not easier.
Whether you’re dealing with hidden calories, unbalanced portions, or sneaky lifestyle habits, this article breaks down the real reasons you might be gaining weight despite eating well. Stick around and we’ll also share tips to break the cycle and finally feel in control of your health.
Before we dive into the ‘why,: let’s talk about what counts as healthy eating. According to the World Health Organization, a healthy adult diet includes:
Plenty of fruit, veggies, legumes (like lentils and beans), nuts, and whole grains such as oats, brown rice, wheat and millet
At least 400g (five portions) of fruit and veg per day, excluding starchy stuff like potatoes and cassava
Less than 10% of your daily energy comes from free sugars (ideally under 5% for extra health benefits). This includes added sugars and those in honey, syrups and fruit juice
Less than 30% of daily energy from fat, with a focus on unsaturated fats (like those in avocado, fish and olive oil) instead of saturated or trans fats
Less than 5g of salt a day (about one teaspoon), and it should be iodised
Sounds spot-on, right? But here's the twist: even the healthiest diets can backfire if something’s off balance.
Eating well means paying attention to both quality and quantity. But even when you do everything ‘right’, weight gain can still creep in. Here’s why that might be happening.
Yes, under-eating can backfire. When your body feels starved, it clings to fat and slows your metabolism, such as a case of chronic starvation. This survival mode makes it harder to shed kilos even if you’re eating clean.
Hormonal imbalances like thyroid issues, PCOS, and even menopause can make it harder to lose weight. If you suspect something’s up, talk to your GP. No amount of salad can fix the issue. These conditions often affect hunger, satiety, fat storage, and energy levels, so medical support is essential.
Scoffing down your meals without really chewing? Research has found that fast eaters are more likely to gain weight and develop metabolic issues like high blood pressure and insulin resistance. Slowing down helps you tune into your hunger cues and may reduce your risk of metabolic syndrome.
Mild dehydration can mimic hunger and lead to unnecessary snacking. Water plays a key role in digestion, energy metabolism, and appetite regulation. If you tend to nibble throughout the day, try tracking your fluid intake—your body might just be thirsty, not hungry.
You’re not imagining it. Meals out with friends or family often mean more food, more alcohol, and more dessert. And because eating socially is enjoyable, we tend to eat more without realising it. Even ‘healthy’ meals can end up being higher in calories when portions or toppings are added.
Skipping meals, especially breakfast, can lead to intense hunger later in the day, often followed by overeating. It can also affect your blood sugar, mood, and cravings. Regular, balanced meals help stabilise your energy and reduce the urge to binge or snack excessively at night.
If you’re unsure whether breakfast really matters, Is Breakfast Important for Weight Loss? explores how your morning meal can influence appetite and long-term progress.
Late-night snacking is common, but your body isn’t great at processing food right before sleep. Studies evaluating the Night Eating Questionnaire (NEQ) as a measure of night eating syndrome have found associations between night eating behaviours and issues like disrupted sleep, altered mood, and stress, factors that may contribute to metabolic dysfunction and weight gain. Also, we are more likely to reach for energy-dense comfort foods when we’re tired or winding down.
Smoothies, juices, almond milk lattes, kombucha, flavoured water and even ‘health’ drinks can pack serious energy. It’s easy to overlook these extras because they don’t feel like meals. But they still count, and over time, they can contribute to weight gain if consumed mindlessly. Large long-term studies actually show that drinks like fruit juice and sugary beverages are linked to gradual weight gain over the years, while replacing them with plain water is associated with less weight gain overall.
Avocado, almonds, hummus, brown rice—healthy, yes. But still energy-dense. Just because it’s ‘clean’ doesn’t mean it’s calorie-free. Portion size still matters, especially if you're aiming for weight loss without tracking every bite. A few ‘health’ extras a day can quietly add up.
Even if you’re eating well, a sedentary lifestyle can slow things down. Sitting for most of the day lowers energy expenditure, reduces muscle tone, and messes with insulin sensitivity. And here’s the kicker: even an hour of intense exercise isn’t enough to undo the effects of being inactive the rest of the day. What helps more? Simply moving throughout the day, like walking, standing, or stretching. It might seem small, but those low-intensity bursts can make a real difference to how your body processes food and burns energy.
We all eat emotionally sometimes. But even ‘healthy’ food eaten mindlessly or in response to emotion can lead to weight gain. Emerging research suggests some medications, like semaglutide, reduce emotional eating by acting on reward circuits in the brain. But you can also explore behavioural tools to help separate emotions from appetite.
Juice cleanses, no-carb weeks, fasting marathons. These restrictive diets might give short-term results, but they usually end in bingeing and weight regain. Worse, they can damage your metabolism over time. The more your weight yo-yos, the harder it gets to maintain a lower set point.
Still wondering what’s behind your weight gain? Read more about the common causes of unexplained weight gain that could be affecting your progress.
Feeling stuck? Here’s how to get back on track without giving up your avo toast.
Include protein and healthy fats in every meal – Helps you feel fuller for longer and supports muscle mass.
Stay active – Move your body daily, whether it’s a walk, dance class, or resistance training.
Improve sleep and reduce stress – Poor sleep and high cortisol = more cravings and slower metabolism.
Watch late-night snacking – Try herbal tea, brushing your teeth early, or shutting the kitchen after dinner.
Talk to a doctor about possible medical causes – Hormones, thyroid, or medications could be playing a role.
Eating healthy is a brilliant first step, but weight loss isn’t just about food choices. It’s about the whole picture: how much you eat, how active you are, how you sleep, your stress levels, and what your body might be going through behind the scenes.
If you’re gaining weight despite eating well, don’t beat yourself up. Use this guide to check in with your habits, talk to a health professional if needed, and take small, consistent steps toward balance.
Ready for a different approach? Discover why Interval Weight Loss is Australia’s No. 1 program for sustainable, science-backed weight loss.
Dr Nick Fuller is the founder of Interval Weight Loss and is a leading obesity expert at the University of Sydney with a Ph.D. in Obesity Treatment. Dr Fuller is also the author of three best-selling books and his work been published in top ranked journals in the medical field, including JAMA, Lancet and American Journal of Clinical Nutrition.