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7 reasons you're experiencing weight gain on a restricted diet

If you’re putting on weight and aren’t quite sure why, this handy guide might just explain things.

7 Reasons You're Experiencing Weight Gain On A Restricted Diet | Juniper

You’re adhering to healthy foods, you’re exercising your bottom off and you’re monitoring your calorie intake — but your weight doesn’t seem to be shifting.

In fact, it might even be increasing. At this point you’re probably thinking to yourself, ‘I keep gaining weight even though I don’t eat much, so what gives?’

Even if you’re doing everything ‘right’, there can still be a few influences you may not be aware of that cause you to gain weight. If you’re putting on weight and aren’t quite sure why, this handy guide might just clarify things.

What is energy balance?

Energy balance is essentially the balance of the energy (calories or kilojoules) that enters your body versus the energy that leaves it. What comes in is composed of food and drink, while what goes out is the energy burned through physical activity.

If the energy you consume is the same as the energy you burn, your weight should stay the same. If you consume more than you burn, it often results in weight gain. And if you consume less than you burn, it can cause weight loss.

However, sometimes, weight loss and weight gain are a little more complex. Perhaps there are lifestyle factors that are affecting your weight, or maybe you’ve got an undiagnosed condition that’s hindering your ability to lose it. There are many things behind unexplained weight gain, which we'll get to shortly.

How can I eat so little and still gain weight?

To that end, here are some of the most common reasons why you might be gaining weight (rapidly or over time) despite being on a restricted diet.

You might not be eating as little as you think

First up, it’s worth considering what your idea of eating ‘little’ actually is. Because, often, people’s perception of not eating much can vary greatly. 

You might be eating less than you used to but still more than your body needs. You might not be eating much during the week but going all out on weekends. Or, you might be skipping a meal here and there but more than making up for it at dinnertime. You could also be forgetting to add things like booze to the equation (alcohol belly is a thing!).

Under-reporting of food consumption is also fairly common. A 1998 survey found that up to 70% of respondents under-reported how much food they ate, especially when it came to junk food intake [1].

Plus, even though your portion sizes may be small, you could be consuming foods that are incredibly high in energy. These can blow out your daily energy intake by a significant amount without you even realising it.

You’re not eating the right foods

On top of high-energy foods, there are other types of food that can make you gain weight.  Highly processed foods are some of the biggest culprits. These usually contain a lot of sugar, salt and saturated fat, and not many of the nutrients your body needs. 

Consuming excess sugar, salt and saturated fat is strongly linked to weight gain [2][3][4]. This is because they’re typically high in calories, however, they also affect your body’s natural ability to maintain weight [5]. 

Research has also found that sugar and fat interfere with your brain’s satiety signals, so it effectively can’t tell when you’re full [6]. This then leads to overconsumption.

Interestingly, a 2019 study found that participants eating an ultra-processed diet consumed 500 calories more than those on a minimally processed diet — despite their meals containing the same amount of calories, sugars, fibre, fat and carbs [7].

You’re not moving enough

While diet plays a huge role in weight loss, inactivity is another key factor. Maybe you’ve cut back your energy intake, but if you’re not moving enough, you can still gain weight.

Research shows that a lack of exercise is one of the main drivers of being overweight or obese [8][9]. Plus, a 2010 study found that participants moved less after reducing their food intake or didn’t compensate for a shift towards a more sedentary lifestyle by consuming fewer calories [10]. Understandably, these participants gained weight.

You're retaining water or dehydrated

Reckon you're drinking enough H2O? If your wee is very dark, you feel tired, you're not going to the loo much or you're feeling bloated, it could be a sign your water intake is inadequate. 

Water consumption affects your hunger signals and your metabolism. Often, when we're slightly dehydrated, we mistake thirst for a feeling of hunger. The symptoms of mild dehydration — trouble concentrating, headache and fatigue — often mirror those of hunger, causing us to eat when we don’t really need to. The result? Consuming more calories than we need.

Adequate water intake also supports metabolic function. In a 2016 study on rodents, increased hydration led to increased metabolism, bringing about a loss of body weight [11]. 

Dehydration can also lead to water retention, as your body holds on to everything it can get. The outcome is swelling on different parts of the body and possibly a higher body weight.

You don't get quality sleep

A lack of sleep can also trigger weight gain. There are several reasons for this: not sleeping enough can drive poor food choices and zero desire to exercise, and it can trigger an imbalance in the hormones that help regulate your metabolism [12].

When you don’t sleep enough, your body increases ghrelin levels and decreases leptin levels. The former hormone makes you feel hungry, while the latter helps you feel full. When these are out of whack, it can obviously encourage increased food consumption. 

You're going through perimenopause

Perimenopause is the period just before menopause hits, often starting when you’re in your 40s. Entering perimenopause can cause fluctuating hormone levels. The outcome is often increased body fat, especially around the midsection.

You’ve got polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) can also trigger weight gain. Women with PCOS typically have insulin resistance, which is where your body has trouble using insulin to convert starches and sugar from foods into energy.

This leads to insulin and glucose stockpiling in your blood and high insulin levels, which then result in an increase in male hormones (androgens). 

On top of hair growth, fluctuating periods, and acne, sudden weight gain (often around the mid-section) is a common side effect of elevated androgen levels.

Can eating too few calories decrease your metabolism?

Another big reason why some people gain weight despite being on a heavily restricted diet? Crash dieting. It may seem counterintuitive, but eating too little can lead to gaining weight.

Crash dieting is where you lose a considerable amount of weight quickly by drastically cutting calories. This could be by eliminating a particular food or food group, skipping meals or eating very small meals throughout the day.

While crash dieting can contribute to weight loss in the short term, it can have negative consequences in the long term [13]. Your body may not get enough nutrients, you put yourself at higher risk of health issues like gallstones, heart problems, and kidney damage, you can lose muscle mass, and you can trigger delayed weight gain [14].

Crash dieting makes your body think you’re starving because of the extreme reduction in energy intake. This can actually slow down your metabolism, as your body goes into starvation mode.

Then, once you resume a normal pattern of eating, you may regain all the weight you lost as your body tries to avoid future starvation.

Healthy ways to help you sustainably lose weight

If you’re keen to steer clear of crash dieting, there are plenty of better ways to lose weight. Here are just a few.

Reduce your calorie intake (safely)

For healthy, sustainable weight loss, there’s no need to skip meals or cut out foods. Instead, aim for 500 fewer calories (or 2092 kilojoules) per day, which is considered a safe amount [15]. This can come from reducing how much you eat or increasing your exercise [5]. 

Wondering how many calories you should eat to lose weight? There is a handy calculator to help you figure out your ideal daily kilojoule intake [16]. Once you’ve figured out the amount required to maintain a healthy weight, simply deduct 500 calories (2092 kilojoules) from that number. And don’t forget to factor in the amount of energy burned through exercise each day, too.

And to track how much energy you’re consuming versus how much you’re expending, you could consider a food-tracking app or tool. Using one of these will also help you gauge your energy intake and output more honestly.

Stick to a healthy diet

Look at what you’re eating and see if you can make any changes. You might notice increased weight loss by eating healthy and adding more whole foods to your diet.

Swap out high-salt, high-sugar, high-saturated fat and processed foods for unprocessed ones like fruits, veggies, whole grains and other healthy foods. Once again, using a food tracking app can assist with monitoring your nutrient intake.

Move more

If you’re not doing much exercise (or none at all) incorporate more physical activity into your day. This will maintain your energy balance or even aid weight loss, along with delivering other health benefits like keeping your muscles and bones strong, reducing the risk of some diseases, and helping you live longer. It may also improve your sleep, which we know affects weight [17][18].

Experts recommend doing at least 30 minutes of exercise most days, ideally every day if you can. This should be moderate-intensity physical activity, but if you’re new to exercise, you can start small [18]. Even 30 minutes of walking can be great for your health and may help you lose weight [19].

Look at other lifestyle factors

Other factors that can hamper your ability to lose weight include poor sleep, dehydration and stress (which often leads to sleeping badly, making unhealthy food choices and hormonal imbalances). Addressing these may help with losing weight.

For better sleep, make your sleep routine more conducive to rest [20]. Create a dark, cool environment in your bedroom, avoid screens right before bed, curb your caffeine intake and move more throughout the day.

Generally, you should drink between 1-2 litres of water per day. However, this number can vary depending on your age, weight and activity levels. This is why thirst can often be a great indicator of hydration rather than sticking to a fixed amount [21].

Put simply, if you’re thirsty or experiencing the signs of dehydration we mentioned earlier, you likely need water. You can also look at your pee to gauge your hydration levels; ideally, you want your pee to be light yellow.

To manage stress levels, you could implement a few lifestyle changes [22]. Things like physical activity, breathing exercises and meditation can help.

Chat to your GP

If you suspect hormones are contributing to your weight gain — perhaps as a result of PCOS or perimenopause — your GP can help. They can measure your hormone levels and recommend ways to manage the issue.

Jump on board a weight loss programme

Juniper’s Weight Reset Programme combines proven medication, health coaching and ongoing support to help you lose weight and keep it off. We prescribe a GLP-1 medication called Wegovy, which contains the active ingredient semaglutide.

Semaglutide is clinically proven to reduce your appetite and make you feel fuller for longer, while also reducing cravings by targeting the rewards centre in the brain. 

For long-term success, changing your eating and movement habits is also crucial, which is why we offer a comprehensive programme that includes 3 core pillars of lifestyle change with the assistance of our UK clinicians.

We can help you break habits that might be impacting your weight and help you hit your weight loss goals sooner.

Image credit: Getty Images


  1. https://pubmed.ncbi.nlm.nih.gov/19094249/
  2. https://www.hopkinsmedicine.org/health/wellness-and-prevention/obesity-sugar-and-heart-health 
  3. https://www.scientificamerican.com/article/the-surprising-link-between-salt-and-weight-gain/
  4. https://medlineplus.gov/ency/patientinstructions/000838.htm
  5. https://theconversation.com/health-check-how-to-work-out-how-much-food-you-should-eat-30894 
  6. https://www.scientificamerican.com/article/how-sugar-and-fat-trick-the-brain-into-wanting-more-food/ 
  7. https://www.nih.gov/news-events/nih-research-matters/eating-highly-processed-foods-linked-weight-gain 
  8. https://med.stanford.edu/news/all-news/2014/07/lack-of-exercise--not-diet--linked-to-rise-in-obesity--stanford-.html 
  9. https://pubmed.ncbi.nlm.nih.gov/10593524/ 
  10. https://pubmed.ncbi.nlm.nih.gov/20384845/ 
  11. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4901052/ 
  12. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2929498/ 
  13. https://www.obesityaction.org/resources/the-risks-of-the-crash-diet/ 
  14. https://www.pennmedicine.org/updates/blogs/health-and-wellness/2018/june/crash-diets-and-weight-loss 
  15. https://www.health.harvard.edu/staying-healthy/calorie-counting-made-easy
  16. https://www.eatforhealth.gov.au/nutrition-calculators/daily-energy-requirements-calculator 
  17. https://www.cdc.gov/physicalactivity/basics/pa-health/index.htm
  18. https://www.betterhealth.vic.gov.au/health/healthyliving/physical-activity-its-important 
  19. https://www.betterhealth.vic.gov.au/health/healthyliving/walking-for-good-health 
  20. https://www.cdc.gov/sleep/about_sleep/sleep_hygiene.html 
  21. https://hub.jhu.edu/at-work/2020/01/15/focus-on-wellness-drinking-more-water/ 
  22. https://www.health.qld.gov.au/news-events/news/how-to-reduce-stress-right-now
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