Sarah Di Lorenzo: Why stress is making you gain weight and what to do about it

There are so many factors beyond diet and exercise that can influence our weight and not knowing the cause of weight gain for many can be completely frustrating.

To fully understand the cause of weight gain you need to really look at the body holistically — sleep, stress, diet, exercise, mental health, genetics and your environment.

Chronic cortisol elevation reshapes metabolism by driving appetite, cravings and abdominal fat storage while breaking down muscle, creating a hormonal environment that quietly favours weight gain over time.

But first, we need to understand cortisol. Cortisol, our primary stress hormone, influences where and how our body stores fat, especially when stress is chronic and sleep and lifestyle are out of balance. When you start to understand this connection it helps shift the narrative from “willpower” to physiology, and opens up another strategy to help lose, manage and maintain weight.

Cortisol also has a positive influence on us — it is one of the key hormones that helps the body wake up and feel alert in the morning.

Cortisol follows a circadian rhythm where levels are lowest at night, begin to rise in the early morning hours and typically peak around the time of waking, helping with our energy and making us feel ready for the day

Cortisol by definition is a glucocorticoid hormone released by the adrenal glands in response to physical or psychological stress via the hypothalamic pituitary–adrenal, or HPA, axis.

When cortisol is released in short small bursts it is adaptive, helping raise blood glucose, mobilise energy stores and keep you alert so you can respond to a threat. This is a survival mechanism.

When we have persistent stress in our lives, cortisol can remain elevated or its normal daily rhythm becomes flattened.

This is where the link to weight gain is. It is this chronic disruption and the weight gain is around the abdomen. This leads to elevated risk of chronic disease.

Cortisol promotes weight gain in many ways. For starters there is an increase in appetite and cravings especially for high-calorie, highly palatable foods rich in sugar and fat. Studies show that people with higher cortisol eat more after stress and are more prone to “stress-induced” snacking leading to weight gain.

There are also changes in how the body stores fat. The fat increase is visceral fat which is the metabolically active fat around the abdominal organs. Visceral adiposity is strongly linked with insulin resistance, type 2 diabetes and cardiovascular disease.

Chronic cortisol elevation also has an impact on our blood sugar and insulin. Cortisol raises blood glucose by stimulating gluconeogenesis (where our body creates glucose) and reducing insulin sensitivity, which makes it harder for cells to take up glucose. Chronic insulin resistance means more fat storage, particularly in the abdomen.

This may also create a vicious cycle of fatigue, cravings and further overeating.

Chronic cortisol is also linked to muscle loss as well metabolic rate. Cortisol breaks down muscle protein to provide amino acids for glucose production.

Then the loss of lean muscle mass lowers resting metabolic rate. So this means fewer calories burned at rest creating a pathway for weight gain over time.

As mentioned, cortisol plays a role in our wake sleep cycle. Cortisol gradually falls over the course of the day and this is the cause for the afternoon slump. When cortisol is elevated in the evening there are levels or loss of the normal peaks and troughs, this again is linked to increased fat cell formation and greater fat mass, even when total caloric intake is similar.

This can really explain why chronic psychosocial stress and shift work are all linked to central weight gain and metabolic complications.

Individuals also can differ in “cortisol reactivity” meaning those people whose cortisol spikes more in response to stress are more likely to stress eat and subsequently gain weight.

From my perspective as a clinical nutritionist, cortisol is one modifiable driver for weight gain but not the sole cause.

Interventions are most effective when I combine strategies to regulate the stress response, that include focusing on sleep and resistance training to protect muscle mass and also focusing on protein in the diet to help stabilise blood glucose, as well as evidence-based stress management techniques.

When I treat clients on prescribed glucocorticoids or living with high chronic stress, it is helpful to set expectations that weight regulation may be more challenging but it’s not impossible, just a slower process.

When you look at weight through a different lens in the context of hormones, nervous system state and metabolic adaptations it can really reduce shame and support more sustainable behaviour change over time and people getting to their health goal, which is what really counts.