How Summer Disrupts Your Metabolic Health

Your metabolic health isn’t just about burning calories; it affects everything from energy levels and sleep to hormones, blood sugar and long-term disease risk.

And while summer is often seen as a ‘healthier’ time, seasonal changes in routine, diet, sleep and stress can quietly disrupt your metabolic balance. Here are four common factors that might be affecting your metabolism this summer and what to do about them.

1. Blood Sugar Swings

Long days, late meals, and sugary snacks can cause repeated blood sugar spikes and dips. This puts strain on your insulin system and leaves you feeling low on energy or constantly hungry.

What happens?

• Glucose may rise, indicating poor short-term blood sugar control, often linked to energy crashes, headaches or brain fog

• HbA1c can increase, showing that blood sugar has been elevated over time, raising your long-term risk of type 2 diabetes

• Insulin may rise if your body is overcompensating to bring down glucose, a sign of insulin resistance, which can lead to weight gain and fatigue

Tip: Eat regular meals with slow-release carbs, lean protein and healthy fats. Carry balanced snacks to avoid crashes and support stable energy.

"An unstable blood sugar interferes with hormones like ghrelin and leptin that regulate hunger and satiety. You may feel hungry even when you've consumed adequate calories because your body is responding to the blood sugar roller coaster rather than actual nutritional needs. The solution typically involves eating regular, balanced meals with protein, high levels of fiber, and replacing refined, processed sugars with more complex carbohydrate sources that provide steadier glucose release, helping maintain more stable energy levels throughout the day. Monitoring glucose, HbA1c, and insulin gives early insight into how your body is coping, allowing for small changes in routine or diet that can significantly improve energy, mood and metabolic resilience."

Dr Thom Philips

2. Increased Heat

Training or simply functioning in hot weather raises internal stress. This can elevate cortisol and interfere with your metabolic balance, making it harder to recover, regulate appetite and manage weight.

What happens?

Cortisol may rise, signalling your body is under stress, which can lead to fat storage, poor sleep and low motivation

• Triglycerides can rise when cortisol is high, increasing the risk of heart disease and metabolic syndrome

• TSH (Thyroid Stimulating Hormone) may increase due to suppressed thyroid function, potentially slowing down metabolism and causing fatigue or low mood

Tip: Train in cooler parts of the day, hydrate well and allow more recovery. Use low-impact sessions when heat is high to support hormonal balance.

"Hot weather adds hidden stress to the body, often raising cortisol levels and disrupting the natural daily rhythm of cortisol production. This loss of healthy diurnal cortisol variation where cortisol should peak in the morning and gradually decline throughout the day can impact everything from your weight to your sleep quality and thyroid function. Tracking these markers over summer helps you understand how your environment is influencing your health and recovery, even when symptoms are subtle"

Dr Thom Philips

3. Sleep Disruption

Warm nights and late bedtimes can reduce deep sleep, a time when your body repairs, resets hormone rhythms, regulates glucose and the only time we produce human growth hormone (HGH).

What happens?

• Insulin may rise due to reduced sensitivity after poor sleep, making it harder to manage blood sugar and maintain a healthy weight

• HbA1c can increase if sleep disruption becomes chronic, linked to poor long-term glucose control

• Cortisol often remains elevated after inadequate rest, promoting cravings and increasing abdominal fat storage

• T3 (free) may fall, reflecting reduced thyroid activity, leading to fatigue, sluggishness and poor temperature regulation

Tip: Stick to a regular sleep schedule, even when routines change. Keep your room cool and limit alcohol or heavy meals before bed.

"It’s a little known fact that the only time the body secretes Human Growth Hormone - crucial for recovery and repair - is during the 1st few hours of deep sleep. Poor sleep in warm weather can blunt this release as well as affecting insulin sensitivity, thyroid balance and your ability to regulate appetite. Testing key metabolic and hormonal markers gives a clear picture of how disrupted sleep may be influencing your energy levels, cravings and overall metabolic health."

Dr Thom Philips

4. Changes in Diet

Lighter meals can reduce intake of protein, healthy fats and micronutrients like B12 and magnesium, all vital for metabolic function.

What happens?

• HDL may drop if healthy fats are too low, reducing cardiovascular protection

• Triglycerides may rise due to reliance on sugary snacks or processed carbs, increasing metabolic and heart health risk

• Vitamin B12 may fall with a lower intake of animal products, leading to fatigue, poor concentration and low mood

• T3 can decline if protein and micronutrient intake drops, slowing down your metabolic rate and energy production

Tip: Choose meals rich in protein and healthy fats, even if smaller. Smoothies, grilled proteins and nuts or seeds can help fill nutritional gaps.

"Lighter summer diets often feature more fruits, vegetables, and salads, which are generally lower in calories and protein compared to heavier, more varied meals. While beneficial for hydration and micronutrient intake, an overreliance on these foods without adequate protein and healthy fats can lead to a reduction in overall protein and energy density. This can result in insufficient intake of essential amino acids and a lower overall caloric intake, potentially impacting energy production and metabolic function over time"

Dr Thom Philips

5. Hydration & Kidney Function

Hot weather increases sweat loss, and if you’re not replacing fluids properly, it can affect kidney function and overall recovery.

What happens?

• Urea may rise with dehydration or higher protein breakdown, indicating the kidneys are under more strain.

• Creatinine levels may become more concentrated, which can reflect lower hydration status or impaired kidney filtration.

• Creatinine can also drop with low protein intake or reduced muscle mass, suggesting under-recovery or lower metabolic activity.

• Creatine Kinase may also be reduced in periods of inactivity or low protein intake, which can impair muscle maintenance and recovery.

Tip: Choose meals rich in protein and healthy fats, even if smaller. Smoothies, grilled proteins and nuts or seeds can help fill nutritional gaps. Aim for steady hydration throughout the day. Include electrolytes in your routine if you’re sweating heavily or training outdoors in the heat.

"Dehydration is common during the summer months and can impact kidney function, muscle recovery and overall metabolic efficiency. Monitoring urea, creatinine and CK helps identify whether your hydration, protein intake and activity levels are supporting or straining your body."

Dr Thom Philips

The Positive Side of Summer

Not all seasonal changes are disruptive. In fact, summer can be one of the best times of year to improve your metabolic health naturally. Longer days, better weather and a shift in routine can lead to positive changes across several key biomarkers, changes worth noticing, measuring and building on.

• Vitamin D levels often rise due to increased sun exposure. This supports immune function, bone strength, hormone regulation and even better blood sugar control. Low levels are common in winter, so summer is an ideal time to restore or build your stores.

• HDL Cholesterol (the “good” kind) may increase with more outdoor movement, lighter meals, and reduced intake of processed foods. HDL helps remove excess cholesterol from the bloodstream and protects cardiovascular health.

• Triglycerides may decrease when you’re more active and eating a fresher, lower-sugar diet. This reflects improved fat metabolism and is a key marker of cardiovascular and metabolic health.

• Cortisol levels can drop if your routine allows for more rest, travel, time outdoors or social connection, all of which support your nervous system and hormonal balance.

• Glucose levels may improve if your summer diet includes more whole foods and fewer processed snacks. Combined with regular movement, this supports more stable blood sugar throughout the day.

Even modest shifts in behaviour can lead to measurable improvements in your health. Testing during this time gives you a clear picture of what’s working well and helps you identify habits worth maintaining long after summer ends.

5 Tips For Naturally Improving Metabolic Health During Summer

1. Start Your Day with Movement

Exercising in the morning, when it’s cooler, can help regulate blood sugar, lower cortisol, and support thyroid function. Even a brisk walk, bodyweight workout, or light jog can boost insulin sensitivity and kick-start your metabolism for the day.

2. Build Balanced Summer Meals

Make the most of seasonal produce by creating meals rich in fibre, lean protein and healthy fats. Salads with grilled chicken or tofu, roasted vegetables with quinoa, or smoothies with berries, seeds and yoghurt are great options.

3. Get Safe Sun Exposure for Vitamin D

Spending 10-20 minutes in direct sunlight (without sunscreen) a few times per week can help boost vitamin D levels naturally, essential for immune health, glucose regulation and mood.

4. Prioritise Sleep, Even When It’s Warm

Quality sleep helps regulate hormones like cortisol, insulin and thyroid hormones. Use blackout blinds, keep your bedroom cool, and avoid heavy meals or screens close to bedtime.

5. Stay Hydrated with Electrolyte Support

Dehydration can impact kidney function and make it harder for your body to process waste, regulate temperature and maintain energy. Add electrolyte tablets to water after exercise or when it’s especially hot.