Diet soda and the 5: 2 intermittent fasting diet

diet chocolate soda

the 5:2 fast diet ™

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Diet soda – yes or no?

As readers of The Fast Diet know, the very best drink on a Fast Day is water – plenty of it, still or sparkling, with nothing added save an ice cube (if the weather ever improves enough to warrant it!). A lemon or lime slice can be nice. If you are looking for flavour, go for herbal tea, green tea, black tea and black coffee – if you add milk, the stealth calories soon add up.

Fruit juice and smoothies, though considered a ‘healthy’ option, in fact contain a lot of fruit sugars and are no replacement for eating the whole fruit, particularly on a Fast Day, when you are looking to avoid anything that will lead to an unwelcome spike in your blood sugars.

Lots of people have asked about The Fast Diet position on fizzy drinks. ‘Full-fat’ sodas are, of course, stacked with sugar – up to 10 teaspoons per can – so it’s no surprise that they should be avoided on a Fast Day. Diet sodas generally rely on aspartame or sucralose for their sweetness. There is some concern about the effects of these intense sweeteners on appetite and gut bacteria, and one study recently linked aspartame with certain blood cancers in men (though not in women).

The answer is that there is no clear answer on diet soda, at least not yet – so exercise caution. If a Diet Coke gets you through a Fast Day, fine. But limit your consumption over the course of a week. And if you’re reaching for the can time and again, reach for the tap too, whenever you can.

I’ve never been a big fan of fizzy drinks, but then I’ve never been a big fan of water either, it never seemed to quench my thirst and tasted a bit funny – we have very hard water down here. So, I always drank squash, not being much of a tea or coffee drinker either. On my first fast I decided to stick to water to save the cals, even though I wasn’t keen on it. The next morning I poured my usual glass of squash and found it far too sweet! Fasting has turned me back on to water and it’s now my drink of choice – love it 🙂 I feel much better for it and am saving money now I only have to buy squash for the husband.

The moral of the story? If you think you’re not keen on water, well just make yourself drink nothing but it for a day. If you’ve the willpower to fast, you’ve the willpower to do that. It may susprise you how you feel about water after just a day on it and away from your usual drinks!

Talking of drinks… Interesting fact: a recent survey found that the average working Briton spends £7.81 a day on lunch, drinks and snacks. Since these are the very things you sacrifice on a Fast Day, your saving in a week could be around £15. That’s £60 in a month. More than enough for a new bikini, right?

There seems to be a persistent rumour that ‘Diet drinks make you fat’ because the chemicals and the manufacturing processes involved affect the body’s ability to break down the food eaten alongside. I am not aware of any actual research into this but if anyone else is I’d be grateful for a link 🙂

@fab50 Have a look on YouTube for the documentary series ‘The Men Who Made Us Fat’, it’s a real eye opener 🙂

Thanks shiningmoogie! Will do.

What beverages other than water are acceptable/not acceptable on fast days? Is wine permitted on non-fast days?

slocol, wine is permitted but of course if you consume excessive calories on non-fast days you won’t lose weight, so I tend to keep it to one glass so as not to sabotage my weight loss efforts. The general rule of thumb is to eat and drink nornally on non-fast days. Good luck!

@slocol: You can drink what you like on a fast day, just as long as you count the calories towards your limit – hence most of us choose 0 cal drinks where possible – water, black tea, black coffee, fruit tea etc. Juices are high in cals so best avoided if you want to eat too! You can have milk in your tea if you count the cals, same for sugar (although best avoided). Some folks like weak squash for a few cals, or even an oxo cube or marmite in hot water for a low cal savoury ‘soup’ drink!

I’ve begun the 5:2 diet second fast day is today and going well!

I am undertaking the diet purely for the health benefits rather than to lose weight, as I am fairly petite weighing 8st 4lbs, height 5ft 0.1″. Waist measurement at smallest part of stomach 28″ and across tummy button widest part 30″. Age 44.

Having said that I the scales in ‘Boots the Chemist’ gave me a reading of B.M.I. 22.6 and a body fat reading of 35.9% (which sounds incredibly high) does anyone know how accurate these machines are regarding body fat.

Also as a petite build will an intake of 500 calories on a fast day be too many for the fast to be effective?

I am really worried about my body fat reading now I am alarmed I have 35.9% body fat – really scary the thought of being TOFI?

All my adult life my weight has been circa 7st 13lbs to 8st 6lbs, I have very rarely ate chocolate, cakes, biscuits, sweets or sugary drinks over the past 30 years. I probably drink two glasses of wine on average per week.

I generally have had a healthy diet on the whole no takeaways fast foods etc, So I am baffled about my 35.9% body fat – could this be purely down to lack of exercise? Please please advise.

Caddie – there are bdy-fat calculations available online which take BMI, age and gender into account. The one I tried for you gave 31.84% fat which is a considerable saving but I would still not trust it – the same formula gave me 22.5% fat but I can hardly pinch anything now, thanks to 5:2. Age based calculations assume that we lose lean mass so the difference must be fat – not always the case if you are active… Not sure how accurate Boots machine is but the impedance-based measurements rely on skin resistance being ‘normal’ – sweaty or dry will chance readings considerably. Pete.

I’ve struggled with my Body Fat%, but I found that this article really shed some light, so I hope it helps:

The guy’s a newly started 5:2 dieter, and seems to be in a similar situation to me, so I’ve found it a good read 🙂

Thanks… but that’s where my worry lies – in the above article on the photographic representation of ladies body fat I look some where between the 25% and 30% photograph. So to have a reading of 35.9% is making me worry I am a TOFI which stands for (THIN on the OUTSIDE FAT on the INSIDE). See page 12 of the FAST DIET book. So my question again is “As a petite build will an intake of 500 calories on a fast day be too many for the fast to be effective to reduce the TOFI excess body fat?

Hi Caddie, I had a similar question when I calculated my estimated calories used every day to be around 1500 – I was thinking I should maybe consume fewer than 500 in order for the diet to ‘work’ – but Michael said to stick to 500 regardless!

Can you use Stevia or Eryitherol sweetners?

Jacqueline – you can certainly use sweeteners if they work for you. I would use Stevia, which is derived from a shrub, over chemical alternatives. I like raw agave nectar too – it is a low-GI sweetener, but you must check the label. Blue raw agave seems best to me. You may find that you lose your sweet tooth after a few months of fasting. I did.

can you add truvia to your green tea?

I drink a lot of diet tonic water, as the caffeine in diet coke wires me. But I mean a LOT of tonic water. I’m thinking maybe I should take a break from it for a week and see whether it makes a difference.

Just started the 5.2 last week and lost 2lbs so far so good.
My question is, if I do not normally eat 2000 calories on the non fasting days how does going down to 500 calories count as a quarter? Should I work out my normal non fasting days calories then cut this back to say 300 calories.

N.ow I’ve been on the diet for one week, and today is another fast day. I find the fast easy – I get hungry from 10:30 until 1 pm, then not. I seem to lose 2 lbs fasting, then gain back one, but yesterday 1 1/2 because of Easter. I think this is going to work

I did my third fast, and have lost 2 pounds, I am pleased !! But this morning after
My third fast I had gained 2 tenth of a pound, I wonder if this is normal?
Any thoughts

I only do soups for my fast days they fill me up and they are easy! I just
Wonder if they are healthy enough

What about Bouillon or similar as a hot drink?

I am completing my third week of the 5.2 Fast diet today. The first Fast day was the only hard day. I did notice that I am not as hungry on non-fast days as I used to be. I am using My Fitness Pal app to track my calories/exercise and that is very helpful. I usually eat less than 1200 calories on the 5 days and the App keeps saying that I will register as in starvation mode. Is this true? I am starting out very overweight (mildly obese) and previous diets have had terrible results. I tend to give up quickly when I check my weight and don’t see the results of my efforts. So I decided I will wait a full month before checking my weight, to avoid discouragement. I do feel that this is a diet that I can follow that will truly change my eating addiction. I do have trouble giving up my skinny latte, but I just adjust my other intake on those days. Thank you for writing this book, which I plan to re-read occasionally.

@elbarnett… I use the Fitness Pal and it’s a very good tool… I think you need to take note of what it’s saying as you can go into ‘starvation’ mode and your body will work hard to maintain your weight … I think 1200 is a good indicator for the non fast days as its still a low amount… I found that because I was less hungry on feast days, 1200 was a lot.. But it’s those foods like pies and sweet stuff that piles on the calories…

I started today after the great program with Dr. Mosley shown on TV. It was a wake up call. I have tried by having appropriate meals for breakfast and lunch and then have a bowl of hearty veggie soup for dinner. It got me started by dropping 7# in 7 weeks.
It can get boring but this system seems to be better because I can place it into my routine with less problems. I have the food there, I just have to portion it on fast day.
I found a long time ago that it was the fizz that I wanted in soda but club soda had sodium. I found a sparkling water that has flavor but no sweetener or sodium. Works in baked goods too. My hubby doesn’t know I sub soda for eggs and shortening. That makes calorie counting easier.
Thanks for the program.

I am embarking on my third month of the diet and it may sound weird to some but I didn’t want to weigh myself first as I didn’t want to get depressed if I didn’t lose any weight. I am size 12 but inching towards a 14 which is a situation I needed to change. I haven’t dieted since I was 16 and always used exercise to control weight. However as a working mother of two children I was getting really low as I could never fit enough exercise hours into my schedule. I have to say the first three weeks were hard and my sleep patterns suffered. However I persevered and really see myself continuing this way of eating forever. I just bought size 10 jeans for the first time in ages and people are starting to comment on my weight loss which is fantastic. I stick to a really boring meal plan and M&S are my NBF! I have no breakfast as I find it makes me hungrier, just black tea, coffee, sparkling water or a Diet Coke. For lunch it’s M&S salmon and potato salad at 240 calories and then dinner is a piece of salmon baked in foil with 1/2 bag of mixed veg with some fresh chilli, ginger, lemon juice and a splash of soy sauce. This works for me as I feel organised knowing I have all the ingredients in the fridge for the week. Hope this helps habit freaks like me, as I think if dieting sounds like loads of hassle it would definitely put me off. I love reading all the tips so please keep them coming.

Myself and my wife were on the Sky TV channel Shop America which promoted the Atkins diet (before the fast diet). Although I do not recommend this any more as a long term solution (mainly because influence on higher IGF1 and protein long term conversion), I would like to say that we have lost a lot of lbs on the fast diet – about 22lbs (10kg in euro blurb) in one month and about 4 stone over 6 months. I just want people to be healthy and I think anythying that gets the weight off to start with in the short term is ok. The fast diet is a great way to go on for life to keep the weight off – VERY important. I am thinking about putting all my experience into self help publication so many can know what I have found out over the last ten years. If you have any stories relevant to Atkins and Fat Diet etc. please let me know at

Loopylou – completely agree that developing good habits is one of the keys to success on the Fast Diet. Knowing what you’re going to eat on a Fast Day really helps – rather than rooting about in the fridge looking for inspiration. The low-cal ready meals M&S are brilliant, and Cook has brought out a range of frozen meals that tick all the Fast Day boxes – things like Chickpea tagine (223 cals) or ‘Thai Chicken patties in aromatic broth’ (320 cals). The Fast Diet Recipe Book is out soon too – I have seen the first copies off the press and I’m thrilled. Alongside all the fresh meals and ideas, the book also includes lots of easy meals that can be made in bulk and frozen in Fast Day portions.

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