Body Clocks and Eating Patterns

Most people eat soon after waking, then graze through the day up to bedtime. This means they may eat over a 16 hour period.

This pattern of eating does not sync with our body clock or circadian rhythms, which some believe may put us at a greater risk of obesity.

Researchers believe that aligning your eating to your body clock could boost your overall health and potentially help you lose weight. The theory is that are bodies are designed to digest and absorb food during a relatively short period of each day, then to repair itself and burn stored fat when we fast. While it is not known whether there is an optimum period during the day or how critical timing is, having less opportunity to eat does seem to lead to less food intake.

A pilot study in 2018 found that by delaying breakfast for 90 minutes, and bringing forward their evening meal by 90 minutes, people lost more body fat than those who kept to no schedule.

If you are new to time-restricted eating, start off eating within a 12 hour window (e.g. 8am to 8pm). If you want to take it further, increase the fasting time to 14 or 16 hours so you eat within a 10 or 8 hour window (e.g. 8am to 6pm, or 10am to 6pm).

Source: Feature in Good Housekeeping, February 2019.

Body Clock Effect on Medications

Your circadian rhythm (the biological clock that governs sleep, hormone production and other processes) means your body responds differently to medications depending on the time of day. Drugs may be less effective or less well tolerated. Drug chronotherapy advocates matching your medication to your circadian rhythm to maximise effectiveness and minimise side effects. (Do not change your drug routine without checking with your doctor or pharmacist first - there may be other factors to consider.)

Some drugs should be taken on an empty stomach because they need to work fast and are more quickly absorbed - while some will only work on an empty stomach as they can bind with food and form a compound that your body cannot absorb. However, several must be taken with food to reduce the risk of side effects, to slow down absorption, or because they can irritate the stomach,

Before breakfast

• Depression meds: disrupted sleep is a common side effect of some selective serotonin re-uptake inhibitors (SSRIs), so it is often recommended that patients take them when they wake up.
• Osteoporosis meds: your body does not easily absorb biphosphonate drugs (e.g. Boniva and Fosamax), so doctors advice taking them on an empty stomach first thing in the morning with a glass of water, then waiting an hour before eating, drinking, or taking other drugs or supplements.
• Antibiotics are usually most effective when taken on an empty stomach when they are not competing with digestion. But some need to be taken with food to help drug absorption, so check first.
• Diuretics should be taken in the morning so you are not kept awake by night-time toilet trips.
• Thyroid hormones taken at this time fit into your body's natural pattern - but should be taken about an hour before eating as food reduces absorption.
• Iron is always best on an empty stomach as food inhibits absorption. However, vitamin C can help absorption so take with a small glass of orange juice.
• Once-daily PPI medicines (proton pump inhibitors) for heartburn or indigestion (e.g. omeprazole) should be taken on an empty stomach before breakfast to reduce acid-production effectively. But H2-receptor blockers (e.g. ranitidine) also inhibit acid production but should be taken after meals.

After breakfast

• Steroids are best taken in the morning when you are naturally more alert, but take them after breakfast to reduce stomach irritation and indigestion.
• Multi-vitamins are best taken after breakfast, as the fat in the meal helps with the absorption of fat soluble vitamins A, D, E and K.
• Take probiotics after breakfast because an empty stomach is too acidic for friendly bacteria to survive. Eating increases the pH in your gut, enabling the friendly bacteria to thrive. But don't wash them down with tea or coffee - hot drinks can kill healthy bacteria.
• Although different diabetes medicines need to be taken at various times of the day (e.g. sulphonyylureas, including gliclazide, should be taken with breakfast), the biguanides (e.g. metformin) can be taken at any time of day but must be taken with or just after food to avoid low blood sugar levels.
• Prescription or over-the-counter decongestant medicine is most effective taken in the morning when symptoms are naturally worse. They also contain a stimulant that may cause sleeplessness.

Mid-afternoon

• Asthma sufferers whose symptoms are worse at night should consider taking a single dose of inhaled steroid in the afternoon to provide a protective night-time effect. 
• BUT as a rule, steroid preventer inhalers (brown canisters) are best taken in the morning and evening.
• Reliever inhalers (blue canisters) are best taken 20 minutes before known triggers, such as exercise. This gives the medication plenty of time to kick in and help prevent an attack.

Best around dinnertime

• Heartburn meds: the stomach produces two to three times more acid between 10pm and 2am than at any other time of day. If you are on an acid-reducing H2 medication such at Pepcid or Zantac, take it 30 minutes before dinner. This controls stomach acid during the overnight period, when secretion reaches its peak.
• Allergy meds: hay fever typically worsens at night and feels most severe in the morning, when levels of symptom-triggering histamine are highest. Once daily antihistamines (e.g Clarityn) reach their peak eight to 12 hours after you take them, so using them at dinnertime means better control of morning symptoms. (Take twice a day antihistamines in the morning and evening.)

After dinner

• Liquid heartburn medications such as Gaviscon are best taken after meals so they sit on top of stomach contents and coat the gullet to help prevent reflux and indigestion.
• If you have morning stiffness and pain with arthritis, take your later dose of anti-inflammatory painkiller after your evening meal to help when you wake in the morning.

Best before bedtime

• Cholesterol meds: cholesterol production in the liver is highest after midnight and lowest during the morning and early afternoon, so statins are most effective when taken just before bedtime. The exception to this is atorvastatin which has a longer half life, so even if it is taken in the morning, it remains active through the night.
• Blood pressure meds: blood pressure is typically higher in the day and lower during sleep. Many people with high blood pressure don't show this dip, especially as they get older. This is a risk factor for stroke, heart attack, and kidney disease. So experts advise taking certain blood pressure lowering drugs at bedtime to normalize daily blood pressure rhythm and decrease these risks. ACE inhibitors and ARBs are most effective when taken before bed.
• One-a-day antihistamines for hay fever are most effective if taken in the evening, as this means medication is at its peak in your system in the morning when symptoms are usually worse. (Antihistamines that need to be taken regularly start acting within 15 minutes so can be taken at any time.)

Timed to symptoms

• Osteoarthritis meds: It's best to take NSAIDs (e.g. naproxen and ibuprofen) approximately six hours before pain is at its worst, so they will kick in at the appropriate time. If prone to afternoon pain, take meds between mid-morning and noon; for evening pain, take meds mid-afternoon; for night-time pain, take meds with your evening meal.

Sources
1: Actually, there's a right time to take 'once a day' drugs by Claire Benoist in Reader's Digest, 2017

2: Body clock myths: when is the best time to take pills? by Michele O'Connor in The Mirror, 23 July 2014

Body Clocks and Mental Powers

Human mental powers vary over 24 hours

• Efficiency in simple tasks (cross out every letter T in a sheet of newsprint) varies with body temperature.
• Memory and verbal reasoning varies with a clock of c. 21 hours.
• Routine repetitive manual tasks (pegs into holes) more successful late afternoon or early morning.
• Brain challenging tasks better late morning or midday.
• Long term memory peaks late in day, short term memory peaks around 10am to 11am.

Jetlag

• Flying from east to west shortens the day; flying from east to west lengthens the day nearer to natural rhythm.
• Tendency to clumsiness and duller mentally; wits recover sooner than dexterity.
• Travellers who stay in hotel rooms take longer to recover than those who go out and meet people.

Health

• Changing shift work schedules: digestion realigns with new sleep/wake cycle relatively quickly; temperature rhythm is next; last is cell division rhythm.
• Worst shift patterns are 12 hour shifts and highly variable ones.
• Workers adapt more easily to later working hours.
• Human rhythms can be changed by changing the meal schedule, with one meal a day. Only breakfast - insulin peaks c. 10am, glucagen c. 11 am, blood iron just before meal. Only dinner, insulin peaks c. 6pm, glucagen c. 11pm, blood iron just before meal.
• Greatest risk of accidents in the two hours before dawn - body temperature and alertness is at its lowest at around 5am.
• Biological clock needs daylight brightness level (10,000 lux on overcast day) to reset each day (candle = 20 lux, electric lamp = 300 lux).

Sources
Jeremy Campbell: Winston Churchill's Afternoon Nap.
BBC2 Horizon: Against the clock, broadcast 2 April 1994.

Body Clocks and Sleep

Sleep habits can affect hormone peaking. Some people have more flexible rhythms and adjust better to unusual work schedules and are good candidates for space missions. Age affects flexibility; it is less easy to adjust in middle age.

Larks feel lively in the morning; body temperature cycles peak early in the day with large differences between top and bottom of the cycle. Suffer more from disturbed sleep if they work at night and when they fly across time zones from east to west. Owls have body cycles that peak later in the day than larks.

Every person has their own typical sleep length, around 8 hours. Sleep has two components - duration and placement. On free schedule study, people slept in fragments, with night time sleep periods typically double the length of day time ones. Between 7am and 2pm or 3pm a 'sleepability gate' opens every 90 to 120 minutes; after 3pm a wide sleepability gate opens and if you have a siesta during this period it is easier to wake from REM sleep than during the night. REM (rapid eye movements) sleep blocks muscle movements and learning memeory and attention stop (impossible to learn while asleep).

Jeremy Campbell: Winston Churchill's Afternoon Nap.

Body Clocks and Health

Biorhythms (body clocks) affect our health.

Circadian (24 hour) biorhythms:

• Blood pressure can rise and fall 20% in 24 hours; lowest first thing in the morning and rises during the day.
• White cell count may rise and fall 50% in 24 hours.
• Pulse rate speeds up in the day and slows at night, by around 10 beats per minute. (The normal resting adult heart beat rate ranges from 60–100 bpm; during sleep a rate of 40-50 bpm is common.)

Circaseptan (about 7 day) rhythms:

• Fluctuations in some body chemicals, blood pressure and heartbeat, acid content of blood, oral temperature, calcium in urine, number of red blood cells, levels of hormone cortisol.
• With kidney transplants, the peaks of rejection are: major peak 7 days after operation; when serum is given to suppress rejection, the peaks are at 7, 14 21 and 28 days, with 28 days the highest risk.
• Response to malaria infection and certain bacteria have 7 day rhythms.
• Pneumonia crisis (before penicillin was available) was usually on the 7th or 9th day.

Timing medication and surgery for best effect:

• Cancer cells have lost their biological clock, so can be hit at any time. 
• Cancer drugs have to minimise harming normal cells, so killing tumour cells should coincide with low point of healthy cell synthesis cycle.
• Anti-cancer drug adriamycin gives fewer side effects when given at 6am as it does in the evening.
• Anti-cancer drug cisplatin should be given late afternoon when potassium secretion is at its highest to avoid toxic effects on the kidneys.
• When sick cells do have rhythms, they are often desynchronised from healthy cells.
• Asthma attacks: the most sensitive time is when lung tubes are at their narrowest in natural rhythms (i.e. just before waking up). Tubes are at their widest at 4pm to 6pm.
• At present medication timing is usually by hospital clock and averages; perhaps in future this may be tailored to the individual's body clock, with the marker rhythm varying with the disease.
• Studies show breast cancer operations give signficantly better results if carried out in the 13 to 28 day part of the menstural cycle.

Shift work

• Heart disease, heart attacks and stomach ulcers are all 2 to 3 times as common in long-term shift workers.
• Conditions such as diabetes are more difficult to control.
• Some shift rotations are worse than others; e.g. 12 hour shifts and highly variable shift patterns.
• There is no perfect shift pattern; larks and owls have different requirements.
• When day and night shifts are permanent, staff turnover drops and accident levels fall.
• Implications for childcare facilities for shift workers.
• Junior doctors in hospitals can be on duty for 36 hours (48 at weekends). [1994]
• Modern treatment means earlier treatment in emergency and accident units, and less opportunity for rest periods when on call.
• One hospital is trying 24 hours on, 24 hours off for both consultants and junior doctors in E&A unit. [1994. Conclusions? Not traced any report on effectiveness.]
• The most extreme shift patterns are in aviation; e.g. 12 day transatlantic schedule. Sleeping in the cockpit not allowed in USA but UK and European regulations allow planned naps. NASA experimented with 40 min rest period in rotation for aircrew and found crew were more alert and less prone to 'microsleeps'.

Jeremy Campbell: Winston Churchill's Afternoon Nap.
BBC2 TV Horizon programme Against the clock, broadcast 2 April 1994