Can Eating Too Little Make Weight Loss Harder? What the Science Says
Updated: Oct 13
Written by Rosy Allan, BSc (Hons), ANutr
Registered Associate Nutritionist | Level 3 Personal Trainer | Level 4 Cancer Exercise Rehabilitation Specialist
For decades, diet culture has encouraged us to believe that eating less is always better.
Smaller portions, lower calorie targets and increasingly restrictive diets have often been presented as the route to achieving a healthier body.
But what happens when someone reduces their food intake so much that they're constantly hungry, exhausted or struggling to maintain their exercise routine?
Can eating too little actually make weight loss harder?
The answer requires an important distinction. A sustained energy deficit is necessary for weight loss, but excessively restrictive diets can have consequences for physical health, muscle mass, exercise performance and the ability to maintain dietary changes.
Let's explore what the science tells us.
Why I believe we need to change the conversation
As a nutritionist and personal trainer, I've worked with clients who have spent years believing that eating as little as possible is the key to managing their weight.
Many have been women who grew up surrounded by unrealistic body ideals and messages encouraging them to take up less space.
I remember growing up during the era of heroin chic, when extreme thinness was regularly presented as something desirable.
As a woman with natural curves, I never felt that my body fitted those expectations. Exercise eventually became a much more positive part of my relationship with my body.
Those experiences have shaped my approach to nutrition coaching.
I don't believe improving body composition should come at the expense of strength, energy, enjoyment of food or physical wellbeing. And while reducing energy intake may be appropriate for some weight-management goals, the aim should never be to eat as little as possible.
Understanding your body's energy requirements
Your body requires energy throughout the day, even when you're resting.
This energy supports essential functions such as breathing, circulation, temperature regulation and the maintenance of body tissues.
Basal metabolic rate (BMR)
Basal metabolic rate describes the energy your body requires to maintain essential physiological functions under standardised resting conditions.
It accounts for a substantial proportion of total daily energy expenditure.
BMR varies according to factors such as age, body size and body composition.
However, BMR is not a universal minimum calorie intake below which everyone becomes unhealthy. Whether a particular energy intake is appropriate depends on the individual's overall requirements, health status, nutritional adequacy and circumstances.
Total daily energy expenditure (TDEE)
Total daily energy expenditure includes several components:
Resting energy expenditure
Physical activity and exercise
Everyday movement, such as walking and household tasks
The energy required to digest, absorb and process food
For adults seeking weight loss, dietary interventions generally aim to create an energy deficit, meaning total energy intake is lower than expenditure (NICE, 2025).
Estimated calorie requirements can provide a starting point, but they're not exact measurements of an individual's metabolism. Energy expenditure also changes over time, which is why nutrition plans sometimes need reviewing.
Does eating too little stop weight loss?
This is one of the most persistent myths in weight management. You may have heard that if you don't eat enough, your body enters starvation mode and stops losing fat. This isn't an accurate description of how weight loss works.
When energy intake remains below energy expenditure over time, the body uses stored energy, contributing to weight loss. However, the energy deficit may become smaller as body weight changes and the body adapts.
What is metabolic adaptation?
During weight loss, energy expenditure usually decreases. Part of this happens because a smaller body generally requires less energy to maintain and move.
There can also be physiological adaptations affecting energy expenditure beyond what might be expected from changes in body composition alone. This is sometimes described as adaptive thermogenesis (Hall, 2018).
However, the size and persistence of these adaptations vary. Metabolic adaptation does not mean the laws of energy balance stop applying, or that eating more will automatically restart fat loss. What it does mean is that the calorie intake that initially supported weight loss may no longer produce the same rate of progress.
Hall and Kahan (2018) also describe biological and behavioural challenges involved in maintaining weight loss, including changes in appetite and energy expenditure.
These adaptations help explain why long-term weight management can be difficult without suggesting that the metabolism becomes permanently damaged.
Why can excessively restrictive dieting become counterproductive?
There are several reasons why eating too little can make a weight-management programme more difficult to sustain.
1. Reduced energy and everyday activity
A very restrictive diet can leave someone feeling tired and less inclined to move.
They may struggle to maintain their normal walking routine, exercise sessions or everyday activities.
Because physical activity contributes to total energy expenditure, changes in movement can affect the size of the energy deficit.
This doesn't happen to everyone, and the magnitude varies considerably.
Nevertheless, energy intake, activity and dietary adherence should be considered together rather than treating calorie targets as fixed numbers (Hall and Kahan, 2018).
2. Loss of fat-free mass
Weight loss does not exclusively involve body fat.
Some of the weight lost can come from fat-free mass, which includes skeletal muscle, water and other non-fat tissues.
A 2025 systematic review and meta-analysis examined 25 randomised controlled trials investigating resistance training during dietary weight loss in adults with overweight or obesity.
The researchers found that adding resistance training helped preserve fat-free mass and produced greater reductions in fat mass compared with dieting alone (Binmahfoz et al., 2025).
The evidence was rated as moderate certainty for fat-free mass preservation and high certainty for the additional reduction in fat mass.
These findings reinforce the importance of considering body composition rather than weight alone.
3. Difficulties meeting nutritional requirements
The less food someone consumes, the more challenging it can become to obtain sufficient protein, essential fats, fibre, vitamins and minerals.
This is particularly important when food choices are highly restrictive.
NICE recommends that dietary approaches for weight management remain nutritionally balanced and take account of personal circumstances, preferences and medical conditions (NICE, 2025).
This does not mean that appropriately supervised lower-energy diets have no clinical role.
However, NICE advises that diets providing 800–1,200 calories per day should only be considered within specified specialist weight-management services, while diets below 800 calories per day require even more restricted clinical indications.
Such approaches should be nutritionally complete, time-limited and medically supported (NICE, 2025).
They are not appropriate as unsupervised, long-term dieting strategies.
4. Hormonal and reproductive health
In some physically active individuals, prolonged or severe under-fuelling can contribute to low energy availability.
This occurs when dietary energy intake is insufficient relative to exercise expenditure, leaving inadequate energy to support normal physiological functions.
The International Olympic Committee identifies problematic low energy availability as an important factor in Relative Energy Deficiency in Sport (REDs).
Potential consequences can include disturbances in reproductive function, reduced bone health, impaired recovery and poorer exercise performance (Mountjoy et al., 2023).
REDs is a specific clinical framework developed primarily for athletic populations. Not everyone following a calorie-controlled diet has REDs.
However, persistent menstrual irregularities, recurrent injuries, significant fatigue or unexplained performance decline should not simply be dismissed as normal dieting symptoms.
These concerns deserve appropriate medical assessment.
Why doesn't the scale always change?
It's important to distinguish between a genuine weight-loss plateau and short-term changes in scale weight.
Body weight can fluctuate because of:
Changes in body water
Glycogen storage
Sodium intake
Menstrual-cycle-related fluid changes
Digestive contents
Changes in medication or physical activity
As a result, the scale may remain stable for several days even when body fat is decreasing.
Over longer periods, a sustained plateau may indicate that energy intake and expenditure are closer to balance than expected.
This doesn't mean someone is necessarily being dishonest about their food intake.
Estimating energy requirements and measuring intake are both imperfect, and factors such as appetite, movement and daily routine can change without someone noticing.
Before responding with further food restriction, it's sensible to review progress over a meaningful period and consider the wider circumstances.
Should you eat below your BMR to lose weight?
There's a common belief that eating below your estimated BMR is always dangerous.
However, BMR is not a scientifically established minimum daily intake that applies to every individual. Clinical weight-management diets sometimes prescribe energy intakes below estimated resting requirements under appropriate professional supervision.
What matters is whether the dietary approach is suitable, nutritionally adequate and safe for the person following it. NICE recommends flexible, individualised dietary interventions rather than applying a single calorie threshold to everyone (NICE, 2025).
For most people seeking sustainable body composition improvements, there is little benefit in pursuing unnecessarily aggressive restriction. A moderate, manageable approach is often more compatible with consistent exercise, nutritional adequacy and long-term dietary adherence.
How can you support fat loss while maintaining strength?
Rather than concentrating exclusively on how little you can eat, consider how your nutrition and activity can work together.
Prioritise adequate protein
Protein provides the amino acids required for maintaining and repairing body tissues, including skeletal muscle.
For healthy, exercising adults, the International Society of Sports Nutrition identifies approximately 1.4–2.0g of protein per kilogram of body weight per day as an intake range sufficient for most individuals seeking to build or maintain muscle (Jäger et al., 2017).
This is sports nutrition guidance rather than a universal recommendation for everyone.
Requirements should be individualised, particularly where medical conditions affect protein needs.
Practical sources include eggs, dairy products, fish, poultry, tofu, beans and lentils.
Include resistance training
Resistance training provides a stimulus for maintaining muscle strength and supporting favourable changes in body composition.
As demonstrated in the 2025 review by Binmahfoz et al., combining resistance training with dietary weight loss can improve fat-mass outcomes and help preserve fat-free mass.
This doesn't necessarily require lengthy gym sessions.
A suitable programme can be designed around individual experience, available equipment and physical capabilities.
Choose satisfying, nutrient-rich foods
Foods containing protein, fibre and water can help create satisfying meals.
For example, vegetables, fruit, potatoes, oats, beans and other minimally processed foods can contribute volume and important nutrients.
The British Nutrition Foundation explains that foods with a lower energy density can allow larger portions for relatively fewer calories, which may help with appetite management (BNF, n.d.).
However, this doesn't mean every meal needs to be cooked from scratch or that convenient foods should be avoided.
A balanced diet needs to be practical enough to fit real life.
Monitor progress without becoming consumed by numbers
Food diaries, calorie tracking and body-weight monitoring can be useful tools for some people.
However, they are not compulsory.
NICE advises considering the risk of disordered eating when recommending weight-monitoring behaviours (NICE, 2025).
If calorie tracking causes anxiety, guilt, obsessive behaviour or increasing food restriction, a different approach may be more appropriate.
Progress can also be assessed through strength, fitness, dietary consistency and other meaningful indicators of health.
When might eating more be appropriate?
There are circumstances where increasing energy intake may be important.
For example, someone who has been following a highly restrictive diet may need to increase their intake to address nutritional inadequacy, support recovery or reduce the health risks associated with prolonged under-fuelling.
A person experiencing menstrual disturbances, significant fatigue, recurrent injuries or unintended weight loss may also need medical or specialist nutritional assessment.
For someone who has reached their body composition goal, gradually adjusting energy intake towards maintenance may be appropriate.
However, increasing calorie intake does not automatically produce additional fat loss.
The reason to increase food intake should be based on an individual's health, nutritional requirements and goals, rather than the idea that eating more magically activates the metabolism.
Final thoughts
Weight management is about far more than eating less and watching the scales.
A sustained energy deficit remains necessary for weight loss, but excessively restrictive dietary approaches can make it harder to maintain physical activity, preserve muscle and meet nutritional requirements.
Metabolic adaptations are real, but they don't mean the body stops responding to energy balance.
The goal should be to establish a dietary approach that supports health, physical function and sustainable progress.
For people looking to improve body composition, that often means combining appropriate energy intake with adequate protein, resistance training and realistic lifestyle changes.
You don't need to eat as little as possible to make progress. You need an approach that supports the body you're asking to become stronger and healthier.
At ROSY, we provide personalised online nutrition consultations and body composition coaching throughout the UK, helping clients develop practical, evidence-based strategies tailored to their individual needs.
Disclaimer: This article is intended for general educational purposes and does not replace personalised medical or dietetic advice. Weight-management approaches should be individualised, particularly for people who are pregnant, breastfeeding, recovering from illness, managing a medical condition or experiencing symptoms of disordered eating.
Persistent fatigue, menstrual disturbances, significant unintentional weight loss or other concerning symptoms should be assessed by an appropriately qualified healthcare professional. People with a current or previous eating disorder should seek specialist support before undertaking restrictive dietary changes.
References
Binmahfoz, A. et al. (2025) 'Effect of resistance exercise on body composition, muscle strength and cardiometabolic health during dietary weight loss in people living with overweight or obesity: A systematic review and meta-analysis', BMJ Open Sport & Exercise Medicine, 11(3), e002363. Available at: https://doi.org/10.1136/bmjsem-2024-002363
British Nutrition Foundation (BNF) (n.d.) Energy density. Available at: https://www.nutrition.org.uk/creating-a-healthy-diet/energy-density/ (Accessed: 13 October 2026).
Hall, K.D. (2018) 'Metabolic adaptations to weight loss', Obesity, 26(5), pp. 790–791. Available at: https://doi.org/10.1002/oby.22189
Hall, K.D. and Kahan, S. (2018) 'Maintenance of lost weight and long-term management of obesity', Medical Clinics of North America, 102(1), pp. 183–197. Available at: https://doi.org/10.1016/j.mcna.2017.08.012
Jäger, R. et al. (2017) 'International Society of Sports Nutrition position stand: Protein and exercise', Journal of the International Society of Sports Nutrition, 14, article 20. Available at: https://doi.org/10.1186/s12970-017-0177-8
Mountjoy, M. et al. (2023) '2023 International Olympic Committee's (IOC) consensus statement on Relative Energy Deficiency in Sport (REDs)', British Journal of Sports Medicine, 57(17), pp. 1073–1097. Available at: https://doi.org/10.1136/bjsports-2023-106994
National Institute for Health and Care Excellence (NICE) (2025) Overweight and obesity management. NICE guideline NG246. Available at: https://www.nice.org.uk/guidance/ng246 (Accessed: 13 October 2026).
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