This article explores the concept of starvation mode, what happens when you diet, the science behind it and whether it is the reason you are not losing weight. There are also some tips to help you progress weight loss diet forward.
The concept of “starvation mode”:
The term starvation mode is popularly used to describe a slowed metabolism in response to calories being lowered. A few key points:
Where does the idea of starvation mode come from?
Anecdotally, it is used by individuals who are not achieving success with their diet i.e. they perceive themselves to be on a diet but are not experiencing the weight loss that they expect. The idea that the body therefore “holds on to fat” can potentially explain their experience.
What happens when you diet?
Reducing calorie intake (enough) results in the following changes – as the body attempts to achieve homeostasis (a state of balance) and subsequently reduces energy output to match the reduction in energy input:
A reduction in energy output from consuming less food
By eating less, you lose less energy through the process of absorbing and digesting food (thermic effect of food).
Body mass decreases
During weight loss, a decrease in body mass results in a reduction of metabolically active tissue, decreasing energy requirements. A greater loss of muscle mass will result in a greater decrease in energy requirements because muscle tissue is more energetically active than fat tissue.
In response to calories being increased or reduced, the body responds by altering its hormone levels. These changes are responsive to energy availability and body mass and are necessary to keep us alive. In the case of creating an energy deficit, thyroid hormones and leptin levels decrease and ghrelin and cortisol levels increase. Lowered thyroid hormone levels are associated with decreased metabolic rate and levels of leptin are associated with levels of body fat. Since body fat levels decrease as weight decreases, leptin levels decrease: leptin is the hormone responsible for signalling to the brain levels of fullness, hence why as you diet, your hunger levels go up! The hunger hormone ghrelin also increases to signal hunger.
You move less
When you have less energy, you quite simply want to expend less energy. This is partly through formal physical activity, such as exercise and also through non exercise activity thermogenesis (NEAT) which consists of activities such as walking and fidgeting. NEAT can be divided into occupational/leisure activities, such as walking, as well as spontaneous physical activity (SPA) such as fidgeting, tapping, just the way that you stand and the energy that you put into it! There is large amount of inter individual variability in SPA, and a great deal of research indicates that NEAT, specifically SPA, is largely genetic and a predictor of weight-gain and may facilitate some individuals being more resistant to weight gain
NEAT may account for 6-10% of total daily energy expenditure in individuals with mainly a sedentary lifestyle, versus up to 50% for individuals with a more active lifestyle (1). In a study where individuals were overfed by approximately 1000 calories per day, this was paralleled by a total energy expenditure (TEE) increase of an average of 554 calories per day – the authors concluded that about 60% of this increase in TEE was due to NEAT! (2).
There is a process termed “uncoupled respiration” whereby instead of energy being generated, something called “proton leak” takes place instead. This essentially means that the process of making energy is inefficient – whilst glucose is still utilised, energy is not produced. This process is more prominent in specific tissues, such as brown adipose tissue (BAT) and skeletal muscle and requires certain proteins (uncoupling proteins UCPs). There are experimental studies that show that during energy restriction, there may be a decrease in levels of BAT and UCPs, increasing metabolic efficiency – effectively meaning that weight loss becomes more challenging.
Adaptive thermogenesis / metabolic adaptation
This term describes the resulting increase or decrease in energy expenditure beyond what would have be expected by changes in body mass. Whilst there is research to suggest that this may occur, it is inconclusive as to the degree to which this may occur – appearing to be highly variable depending on the individual, and not necessarily present in weight stable individuals.
A study on 171 overweight women showed metabolic adaptation to account for an average difference of approximately 50-60 calories and that this was not sustained at a 1-2 year follow up and therefore not predictive of weight regain (3). This was supported by another study that showed a metabolic adaptation of approximately 90 calories whilst individuals were in a negative energy balance, which was then reduced to 38 calories after 4 weeks of weight maintenance (4). The authors propose the argument that metabolic adaptation is not a driver of weight regain or to get the body back to initial weight, since otherwise it would persist post weight loss, regardless of the energy balance of the individual, and that a larger metabolic adaptation would be associated with more weight regain in the long term.
The infamous study from the “Biggest loser” contest showed an average of an approximate 500 calories lower than predicted resting metabolic rate after a 6 year follow up (5). However, other studies have reported no difference in resting metabolic rate (6) and no consistent evidence of a significantly lower resting energy expenditure than predicted (7). What might explain the differences observed between studies? Genetics, rate and method of weight loss, sex, race, physical activity, hormonal and metabolic profiles. Research indicates a large variability in adaptive thermogenesis: for individuals who have lost similar amounts of weight and maintained this weight loss, some of them exhibit a lower energy expenditure than expected, whilst some of them exhibit a higher energy expenditure than expected (-257 calories to +163 calories) (7).
The large variability in NEAT between individuals is likely to be a significant contributor to the differences observed in adaptive thermogenesis. In a study where 16 lean individuals were overfed by 1000 calories per day, there was a 10-fold variation in fat gain and an 8-fold difference in changes in NEAT (2). This change in NEAT was directly predictable of the individuals resistance or vulnerability to body fat accumulation.
Can adaptive thermogenesis / metabolic adaptation stop you from losing weight?
For weight loss to come to a halt, you would need to experience a larger than expected reduction in resting metabolic rate, to offset your caloric restriction. The research indicates that in some cases adaptive thermogenesis may be a contributing factor to a requirement to increase your energy deficit, however, there are many other factors that are likely much greater significant contributors to a slowing in weight loss (a reduction in NEAT may or may not be determined as part of metabolic adaptation). Ultimately, it will be a combination of factors rather than one single factor, that may result in weight loss coming to a halt, and the need to create a greater energy deficit.
Tips to reduce potential adaptive thermogenesis / metabolic adaptation:
Periodic dieting: periods of eating at maintenance calories, known as a “diet break” may reduce the degree of potential metabolic adaptation since it may be associated with the extent of weight loss (8)
Refeeds: a brief period of overfeeding where calories are increased, slightly above maintenance, primarily from carbohydrate, may temporarily increase leptin levels and stimulate metabolic rate. Research indicates that leptin is acutely responsive to short term over-feeding, particularly carbs (9) and energy expenditure may increase moderately, with a study showing a 7% increase in total daily energy expenditure (TDEE) (10).
Reduce calories gradually: large calorie deficits are likely to reduce lean body mass to a greater extent and therefore contribute to a greater metabolic adaptation (11).
Incorporate resistance training: a structured resistance training may reduce the loss of lean body mass (12) and therefore assist with reducing potential metabolic adaptation.
Choose a high protein diet: sufficient protein intake is key for preserving lean body mass (14). Protein is the macronutrient with the highest thermic effect and a high protein diet may contribute to counteracting the effects of adaptive thermogenesis. A study on overweight individuals showed that a high protein diet in comparison to a medium protein diet let to a negative energy balance and may counteract adaptive thermogenesis at -34 months post weight loss (15).
Increase NEAT: whilst it may be challenging to objectively measure SPA, you can increase leisure activity movement such as walking by simply tracking your steps. Whilst this may not be fun, it is an objective way to increase and sustain NEAT, and offset adaptive thermogenesis.
Reasons why you’re not losing weight:
If you’re not losing weight, and you thought it was because you were in starvation mode, then here are some alternative reasons.
Not creating a sufficient energy deficit: whether you’re experiencing adaptive thermogenesis or not, an energy deficit is required to lose weight, which requires reducing calories. An energy deficit needs to be created that is sufficient for you as an individual and this will likely differ to the person next to you.
Tip: create a calorie deficit in the range of 15-25%, or shoot to lose 0.5-1% of bodyweight per week. A combination of a calorie deficit and increasing energy output (formal exercise and NEAT – so get those steps in) is most effective for sustaining weight loss.
Not tracking calories accurately: research indicates that people are notoriously bad at reporting caloric intake and that calories are often underestimated by approximately 37% (15).
Tip: to gain an understanding of what you’re consuming, measure, track and record what you eat for a week or two. Observe what your weight does on that amount. If you are maintaining weight on this amount then you know that you need to reduce what you eat slightly. If you don’t like tracking calories, then keep your diet relatively consistent so that you can more easily adjust your intake – you could simply reduce a snack or a serving of fat. Reducing the amounts of times that you eat out can reduce this variability too!
You’re retaining water: if you’ve just started your weight loss journey or you’re plateauing, it may be due to water retention. Factors such as stress, lack of sleep, fibre intake and menstrual cycles can all significantly contribute to water retention and temporarily inflate levels of weight.
Tip: consider stress levels and if whether you’re cutting calories too aggressively, stressed at work and hitting the gym hard all the time. Try cutting one of them back a bit and introducing more chill time. Also consider fibre intake, menstrual cycles and sleep and track and record your body weight over a period of time and take an average, to take into account fluctuations.
Starvation mode is commonly cited as a reason for lack of weight loss because calories are “too low”: by definition, if weight loss is not occurring, an energy deficit is not being created and therefore either energy output needs to be increased, or increased alongside calories being decreased.
The term starvation mode is used interchangeably with the term metabolic adaptation/adaptive thermogenesis: which describes the greater than expected change in metabolic rate that occurs in response to either an energy increase or decrease. There is scientific research to support that this concept may exist, but the degree to which it occurs, its significance and how long it lasts, are highly variable and depend on the individual and other factors e.g. the diet and energy deficit created.
If you are not losing weight and want to: then it is highly likely that you are not creating a sufficient energy deficit. You can create an energy deficit by reducing caloric intake and increasing energy output – both via formal exercise and NEAT.