Intermittent fasting has become a popular dietary approach to help people lose or manage their weight. It has also been promoted as a way to reset metabolism, control chronic disease, slow ageing and improve overall health.

Meanwhile, some research suggests intermittent fasting may offer a different way for the brain to access energy and provide protection against neurodegenerative diseases like Alzheimer’s disease.

This is not a new idea – the ancient Greeks believed fasting enhanced thinking. But what does the modern-day evidence say?

First, what is intermittent fasting?

Our diets – including calories consumed, macronutrient composition (the ratios of fats, protein and carbohydrates we eat) and when meals are consumed – are factors in our lifestyle we can change. People do this for cultural reasons, desired weight loss or potential health gains.

Intermittent fasting consists of short periods of calorie (energy) restriction where food intake is limited for 12 to 48 hours (usually 12 to 16 hours per day), followed by periods of normal food intake. The intermittent component means a re-occurrence of the pattern rather than a “one off” fast.

Food deprivation beyond 24 hours typically constitutes starvation. This is distinct from fasting due to its specific and potentially harmful biochemical alterations and nutrient deficiencies if continued for long periods.

4 ways fasting works and how it might affect the brain

The brain accounts for about 20% of the body’s energy consumption.

Here are four ways intermittent fasting can act on the body which could help explain its potential effects on the brain.

1. Ketosis

The goal of many intermittent fasting routines is to flip a “metabolic switch” to go from burning predominately carbohydrates to burning fat. This is called ketosis and typically occurs after 12–16 hours of fasting, when liver and glycogen stores are depleted. Ketones – chemicals produced by this metabolic process – become the preferred energy source for the brain.

Due to this being a slower metabolic process to produce energy and potential for lowering blood sugar levels, ketosis can cause symptoms of hunger, fatigue, nausea, low mood, irritability, constipation, headaches, and brain “fog”.

At the same time, as glucose metabolism in the brain declines with ageing, studies have shown ketones could provide an alternative energy source to preserve brain function and prevent age-related neurodegeneration disorders and cognitive decline.

Consistent with this, increasing ketones through supplementation or diet has been shown to improve cognition in adults with mild cognitive decline and those at risk of Alzheimer’s disease respectively.

2. Circadian syncing

Eating at times that don’t match our body’s natural daily rhythms can disrupt how our organs work. Studies in shift workers have suggested this might also make us more prone to chronic disease.

Time-restricted eating is when you eat your meals within a six to ten-hour window during the day when you’re most active. Time-restricted eating causes changes in expression of genes in tissue and helps the body during rest and activity.

A 2021 study of 883 adults in Italy indicated those who restricted their food intake to ten hours a day were less likely to have cognitive impairment compared to those eating without time restrictions.

3. Mitochondria

Intermittent fasting may provide brain protection through improving mitochondrial function, metabolism and reducing oxidants.

Mitochondria’s main role is to produce energy and they are crucial to brain health. Many age-related diseases are closely related to an energy supply and demand imbalance, likely attributed to mitochondrial dysfunction during ageing.

Rodent studies suggest alternate day fasting or reducing calories by up to 40% might protect or improve brain mitochondrial function. But not all studies support this theory.

4. The gut-brain axis

The gut and the brain communicate with each other via the body’s nervous systems. The brain can influence how the gut feels (think about how you get “butterflies” in your tummy when nervous) and the gut can affect mood, cognition and mental health.

In mice, intermittent fasting has shown promise for improving brain health by increasing survival and formation of neurons (nerve cells) in the hippocampus brain region, which is involved in memory, learning and emotion.

There’s no clear evidence on the effects of intermittent fasting on cognition in healthy adults. However one 2022 study interviewed 411 older adults and found lower meal frequency (less than three meals a day) was associated with reduced evidence of Alzheimer’s disease on brain imaging.

Some research has suggested calorie restriction may have a protective effect against Alzheimer’s disease by reducing oxidative stress and inflammation and promoting vascular health.

When we look at the effects of overall energy restriction (rather than intermittent fasting specifically) the evidence is mixed. Among people with mild cognitive impairment, one study showed cognitive improvement when participants followed a calorie restricted diet for 12 months.

Another study found a 25% calorie restriction was associated with slightly improved working memory in healthy adults. But a recent study, which looked at the impact of calorie restriction on spatial working memory, found no significant effect.

Bottom line

Studies in mice support a role for intermittent fasting in improving brain health and ageing, but few studies in humans exist, and the evidence we have is mixed.

Rapid weight loss associated with calorie restriction and intermittent fasting can lead to nutrient deficiencies, muscle loss, and decreased immune function, particularly in older adults whose nutritional needs may be higher.

Further, prolonged fasting or severe calorie restriction may pose risks such as fatigue, dizziness, and electrolyte imbalances, which could exacerbate existing health conditions.

If you’re considering intermittent fasting, it’s best to seek advice from a health professional such as a dietitian who can provide guidance on structuring fasting periods, meal timing, and nutrient intake. This ensures intermittent fasting is approached in a safe, sustainable way, tailored to individual needs and goals.

Hayley O’Neill, Assistant Professor, Faculty of Health Sciences and Medicine, Bond University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

We all want to eat healthily, especially as we reset our health goals at the start of a new year. But sometimes these plans are sabotaged by powerful cravings for sweet, salty or carb-heavy foods.

So why do you crave these foods when you’re trying to improve your diet or lose weight? And what can you do about it?

There are many reasons for craving specific foods, but let’s focus on four common ones:

1. Blood sugar crashes

Sugar is a key energy source for all animals, and its taste is one of the most basic sensory experiences. Even without specific sweet taste receptors on the tongue, a strong preference for sugar can develop, indicating a mechanism beyond taste alone.

Neurons responding to sugar are activated when sugar is delivered to the gut. This can increase appetite and make you want to consume more. Giving into cravings also drives an appetite for more sugar.

In the long term, research suggests a high-sugar diet can affect mood, digestion and inflammation in the gut.

While there’s a lot of variation between individuals, regularly eating sugary and high-carb foods can lead to rapid spikes and crashes in blood sugar levels. When your blood sugar drops, your body can respond by craving quick sources of energy, often in the form of sugar and carbs because these deliver the fastest, most easily accessible form of energy.

2. Drops in dopamine and serotonin

Certain neurotransmitters, such as dopamine, are involved in the reward and pleasure centres of the brain. Eating sugary and carb-rich foods can trigger the release of dopamine, creating a pleasurable experience and reinforcing the craving.

Serotonin, the feel-good hormone, suppresses appetite. Natural changes in serotonin can influence daily fluctuations in mood, energy levels and attention. It’s also associated with eating more carb-rich snacks in the afternoon.

Low carb diets may reduce serotonin and lower mood. However, a recent systematic review suggests little association between these diets and risk for anxiety and depression.

Compared to men, women tend to crave more carb rich foods. Feeling irritable, tired, depressed or experiencing carb cravings are part of premenstrual symptoms and could be linked to reduced serotonin levels.

3. Loss of fluids and drops in blood sugar and salt

Sometimes our bodies crave the things they’re missing, such as hydration or even salt. A low-carb diet, for example, depletes insulin levels, decreasing sodium and water retention.

Very low-carb diets, like ketogenic diets, induce “ketosis”, a metabolic state where the body switches to using fat as its primary energy source, moving away from the usual dependence on carbohydrates.

Ketosis is often associated with increased urine production, further contributing to potential fluid loss, electrolyte imbalances and salt cravings.

4. High levels of stress or emotional turmoil

Stress, boredom and emotional turmoil can lead to cravings for comfort foods. This is because stress-related hormones can impact our appetite, satiety (feeling full) and food preferences.

The stress hormone cortisol, in particular, can drive cravings for sweet comfort foods.

A 2001 study of 59 premenopausal women subjected to stress revealed that the stress led to higher calorie consumption.

A more recent study found chronic stress, when paired with high-calorie diet, increases food intake and a preference for sweet foods. This shows the importance of a healthy diet during stress to prevent weight gain.

What can you do about cravings?

Here are four tips to curb cravings:

1) don’t cut out whole food groups. Aim for a well-balanced diet and make sure you include:

• sufficient protein in your meals to help you feel full and reduce the urge to snack on sugary and carb-rich foods. Older adults should aim for 20–40g protein per meal with a particular focus on breakfast and lunch and an overall daily protein intake of at least 0.8g per kg of body weight for muscle health
• fibre-rich foods, such as vegetables and whole grains. These make you feel full and stabilise your blood sugar levels. Examples include broccoli, quinoa, brown rice, oats, beans, lentils and bran cereals. Substitute refined carbs high in sugar like processed snack bars, soft drink or baked goods for more complex ones like whole grain bread or wholewheat muffins, or nut and seed bars or energy bites made with chia seeds and oats

2) manage your stress levels. Practise stress-reduction techniques like meditation, deep breathing, or yoga to manage emotional triggers for cravings. Practising mindful eating, by eating slowly and tuning into bodily sensations, can also reduce daily calorie intake and curb cravings and stress-driven eating

3) get enough sleep. Aim for seven to eight hours of quality sleep per night, with a minimum of seven hours. Lack of sleep can disrupt hormones that regulate hunger and cravings

4) control your portions. If you decide to indulge in a treat, control your portion size to avoid overindulging.

Overcoming cravings for sugar, salt and carbs when trying to eat healthily or lose weight is undoubtedly a formidable challenge. Remember, it’s a journey, and setbacks may occur. Be patient with yourself – your success is not defined by occasional cravings but by your ability to manage and overcome them.

Hayley O’Neill, Assistant Professor, Faculty of Health Sciences and Medicine, Bond University

This article is republished from The Conversation under a Creative Commons license. Read the original article.