Some thoughts on fasting

Most ‘official’ advice adheres to the calories-in/calories out-theory. It underlies their understanding of how a healthy weight is maintained. Calorie-control is, in their view, a zero-sum thing, it is a form of energy accountancy, and fasting is, in their view, just another faddish way of eating fewer calories. And worse, fasting has become an even more significant fad since the health journalist and broadcaster Dr. Michael Mosely investigated it in a programme which was shown in the UK and world-wide on BBC TV (1). Even worse, Moseley’s programme was followed by a hugely successful book co-written with Mimi Spencer – The Fast Diet (2).

For the Official diet experts intermittent fasting is just another stupid diet fad, something to laugh at; something to ridicule. But curiously, huge numbers of people who have tried it for themselves have found that it can work, and work well. You can lose weight by fasting periodically. A quick disclaimer here. I am not advising anyone to undertake Intermittent Fasting. In fact, I think switching to a low-carb Beating Diabetes eating regime alone would benefit the health of most people who currently adhere to Official diet guidelines. It is up to you, but read on to discover what it is all about, and why I believe Intermittent Fasting has significant potential benefits, why it may turbo-charge the low-carb approach.

So, what is Intermittent Fasting? Is it just a fancy way of cutting calories, or is it doing something completely different? Well, you are now familiar with the various options the body has at its disposal to keep us constantly supplied with energy. Eating is the most common method, obviously, but, as you can see, we can function between meals quite nicely without consuming any food at all. Mosely and Spencer’s fasting method isn’t actually a total fast at all. They simply advise that, for two days each week, followers cut their food calorie intake down to around 500 for women, 600 for men (UPDATE: the most recent book on The Fast Diet has upped the calorie limit to 800/day). They do not even advise whether those calories should be low-carb or not, nor whether they should be consumed in one, two or even three meals across the fast-day. And because for the other five days of the week followers can eat normally, their method is called the 5:2 Diet. I have encountered many people, family members included, who have discovered it for themselves. They just started practising the 5:2 approach off their own bat, without permission from their dieticians or doctors and found it a pretty painless way to lose weight. In fact, because it is a diet that the Official guidelines and legions of health professionals neither promote nor advise, I call it a people’s diet. 5:2-ers, it seems, know something that many of their doctors and dieticians do not.

The 5:2 and other similar diets may result in a small reduction in calorie intake, but over the week as a whole, the absolute calorie reduction is minimal. In my view, it works not because it induces a “calorie deficit” but rather because it switches the body’s energy supply from the food-glucose mode, through glycogen and into its fat-burning modes. It therefore reliably reduces insulin production and allows, for a day or two each week at least, one’s body chemistry to recover. It is about body chemistry, not calorie accountancy. Remember, it is difficult to store fat in the absence of insulin, and you cannot lose fat in its presence.

I tried the 5:2 myself once and I was quite pleased with the result. It did help me to lose some weight, even though my overall weekly calorie intake didn’t change much. I ate a little more on post-fast days, I suppose. I chose to do my fasts on busy days. I figured that being busy would distract me from my stomach’s grumblings, which in fact, it did. Eventually, however, I found that my will power became a problem and I stopped. Fasting during the day was not an issue, but when I got back home for my evening meal, I lapsed. Most people, it seems, are stronger willed than I and have learned to celebrate those brief sensations of hunger for what they are: a sign of the body switching over to fat burning.

But there are many other ways to fast. Currently I have found another one that suits me much better. Like those Hindu fasters mentioned earlier, I simply skip breakfast most days. I try to eat my evening meal the night before as early as I can (usually around 8pm although earlier still would be better still). I particularly choose low-carb ingredients for that meal then eat nothing until noon the next day, or sometimes later. I guess it regularly leaves me food-glucose free for around 16 hours at a stretch. This seems to work for me and is a method I find very easy to apply. My understanding of its mechanism (how it works, in other words) is that the evening meal does not evoke much of a glucose-insulin response. This allows me to enter my natural overnight glycogen burning mode before I even go to bed. Then, sometime around dawn, when my glycogen tank runs out, I switch over to fat burning. I carry on fat-burning after I rise through until I break my fast around noon or 1 pm. I will drink during this time and have water, tea or coffee with a dash of milk (a small carb dose here), but it works. It is a short absolute fast rather than a longer relative one like the 5:2 diet, but, like the 5:2, it is Intermittent. I can eat normally when I am not fasting. I am not on a starvation programme.

More demanding fasting regimes might include ones where followers have a partial or total fast every other day; not something for weak-willed people like me. Another is known as the 8-Hour Diet. (see Table 6.2 for a bird’s-eye view of various fasting options). It requires its followers to eat all their meals within an eight-hour period, between 10 am and 6 pm say, or 12 noon and 8 pm, for example. For the other sixteen hours, they eat nothing but may drink water. This is also called “restricted eating” and it is, more or less, my current habit. But all these fasts all end up doing just one thing to a greater or lesser extent. They switch insulin off and turn the fat-burning mode on.

The one thing that modern fasting isn’t is starvation. Fasting switches fuel sources around allowing insulin levels to drop and fat to be mobilised. Although these changes also occur during starvation several other less desirable adaptations to severe food restriction happen as well. Firstly, the body senses it is entering a starvation state and starts to economise. It will slow down its metabolic rate causing lethargy and a feeling of cold. Secondly, it diverts its conscious priorities towards food-seeking. People become obsessed about food and it will occupy their thoughts intrusively. And thirdly, if sugary, starchy and protein foods are limited during starvation the body begins to convert some of its own proteins into glucose causing a loss of muscle mass. Fat cannot be converted back into glucose in any meaningful amounts. Starving people will waste away. Those who fast do not experience these drastic starvation-type effects because their dietary protein intake will be sufficient to produce glucose without the need to degrade muscle tissue, even if they do not consume any carbs at all.

Is this relevant to Beating Diabetes? The answer is yes because a form of starvation therapy is currently advocated as a means of putting diabetes into remission. It is called very low-calorie (VLC) food replacement therapy. This involves cutting daily calorie intake to around 800/day, less than half the usual daily requirement for health. The replacements usually come in the form of liquid shake drinks or soups. Apart from the shake nothing else should be consumed other than perhaps mineral and vitamin supplements. I consider this approach to be a form of ‘chemotherapy’ for diabetes, and one which requires quite intense motivational and supportive care from a health professional. The thing is it does work for some people. Some people lose weight and do indeed see their diabetes remit. But, it is a very big ask. Lethargy and coldness are quite common side effects and a course of meal-replacement liquids are not real foods. For those who reach their target weight and HbA1 level, and their VLC diet comes to an end, there is another dilemma. What next? Returning to their old diet habits will almost always be followed by a gain in weight and a relapse back into diabetes. For those who chose to adopt the Official dietary advice, there is a risk that they too will relapse because Official advice is to give large quantities of carbohydrate foods to people known in this case to be carbohydrate intolerant. The best follow-on diet would appear to be to adopt a low-carb approach and maintain it indefinitely. So, I wonder, why not forget about starvation therapy with VLC meal replacement shakes and just go low-carb with real food from the outset?

Fasting on the other hand has a long and venerable history. “Fasting unto prayer” has been used as a religious practice across the world and throughout history, and for a very good reason. It helps clarify the mind and improves perception. In pre-historic times, fasting may not have been a lifestyle or even a religious choice, it would at times have been a harsh fact of life. Another name for it may have been a “hunger”. We humans are adapted to function very efficiently and effectively when hungry; in times past, it drove us to hunt or forage more intently. If hunger had clouded the mind and left us listless, we would have died in lean times. In fact, hunger/fasting was probably the rule rather than the exception for many of them back then. Problem is, we modern humans have precisely the same biology as our ancestors, but now live with large well-stocked fridge-freezers, cupboards full of packaged and tinned food, and a convenience store on a nearby street. Intermittent Fasting and Restricted Eating, it seems, are potential ways to slide our body chemistry back into a more natural and healthy glucose-insulin-lite mode, the one, in fact, we evolved to thrive on.

Bottom line – Intermittent Fasting works for many people. People lose weight with it and say they feel healthier. It just requires some thought about how to do it, some planning how to make it work; how to prolong glycogen burning and perhaps get into the fat-burning modes. The only people who it may not be advisable for are children, those with medical conditions, and particularly those on certain medications, especially medications for diabetes. They would all need to check things out with their doctor first, and good luck to them with that. Some would also include pregnant women on that list. Hmmmmm… it is less risky for doctors and writers to play safe. But let’s face it gestational diabetes is now running at epidemic proportions too. Since 1980, when our nation’s diets flipped and became low-fat and high-carb, one US study reckons gestational (pregnancy-related) diabetes rates have risen 35-fold, a 3500% rise.

One final thought – can fasting be used to outweigh or counterbalance the detrimental effects of a high-carb diet? My hunch is probably not for most people. Constantly flip-flopping from high-carb to fasting does not allow the body to power itself consistently without the taint of insulin. So, having fasted, let us think (briefly) about exercise. Can you walk, run or swim yourself out of diabetes? Spoiler alert – no. But, physical activity does burn muscle glycogen, which has to be replaced. Exercise can be an insulin-sparing activity.

Table 6.2 Fasting; à la carte

    Intermittent fasting (IF)The Fast Diet (The 5:2)Pick two days each week and cut your intake food right down to 500Cals a day (600Cals for men). This is relative, not absolute, fasting. No requirements stated about how many meals or what sorts of foods you eat; just cut the cals on “fast days”
 Alternate day relative fastingMuch the same as the 5:2 but done 3 or 4 days each week
    Absolute fastingThe late, late breakfastBasically, extend the period of time between your evening meal to the breaking of your overnight fast the next day. Aim for 14-hour (or more) fasts. Water is allowed
 The 8:16Much the same as the late, late breakfast but all your eating is done over just 8 hours of the day; say between 11am and 7pm. Nil by mouth for the remaining 16 hours, though water is allowed.
 The 4:20Much the same as the 8:16 but food is squeezed into just four hours; say from 1pm to 5pm though water is allowed at any time
 Alternate day absolute fastingNil by mouth every other day though drinking water is allowed
 2-, 3- or 4-day fastsMuch the same as alternate day fasting but extending the duration of each fast. Water is allowed. This method will move you into benign dietary ketosis
  • There is, of course, nothing to stop one from mixing and matching. Say, 3 late breakfasts and 1 or 2 low-cal “fast days” in a week
  • It is likely that choosing low-carb foods between periods of fasting will magnify the effects of the fast, and over time help correct insulin resistance

Table 6.3 Who should consider fasting? A hunch too far?

StatusFeaturesDietary need
Insulin sensitiveHealthy*, normal weightLowish carb/Low-GI
Insulin dominatedHealthy, overweight**Low carb/GI + IF
Insulin resistantMetabolic syndrome***, pre-diabetes/T2DM, and overweight/obeseStrict Low carb/GI + IF

GI – glycaemic index. Low-GI basically means a low sugar, low starch type diet…basically the Beating Diabetes approach

IF – intermittent fasting

T2DM – Type-2 Diabetes Mellitus

* Healthy includes full blood check results being normal too (blood pressure, triglycerides, HbA1, uric acid, possibly also ultrasound san of liver and pancreas)

** Note: weight and health problems are not necessarily linked. Some people are healthy and overweight. Others have normal weight but are unhealthy. They can be TOFIs – thin on the outside, fat on the inside. Actually, recent opinion says being overweight is not healthy even if the person currently appears to be so

*** The Metabolic Syndrome is a constellation of physical and chemical disorders linked to Insulin Resistance. Various definitions exist but commonly they would include overweigh/obesity, raised blood pressure, raised glucose levels (especially fasting glucose and after a glucose drink), and raised blood triglyceride fat levels. Some also include abnormal cholesterol levels, gout, non-alcoholic fatty liver disease (NAFLD) and in women the polycystic ovarian Syndrome (PCOS).


  • Dr. Michael Mosely investigated it in a programme called “The power of intermittent fasting”. It was shown in the UK and world-wide on BBC TV.
  • The Fast Diet Michael Moseley and Mimi Spencer. Short Books Ltd; Revised and Updated edition (18 Dec. 2014) Note: check out his new 800 calorie 5:2 diet.