One Week Flat

7 sachets |1 week's supply

4.2/5 (85 reviews) Read verified product reviews
4.2/5 (85 reviews) Read verified product reviews
Camilla Gray DipCNM Nutritional Therapist
My personal discovery of live cultures started with ‘One Week Flat’ 10 years ago and it’s one I still use and recommend regularly, especially before holidays or festive periods.
Camilla Gray
Camilla Gray DipCNM Nutritional Therapist

Who is it for?

Optibac One Week Flat is an affordable, 7-day course of friendly bacteria in easy-to-take sachets. It is gluten-free and therefore may be suitable for those with bloating.

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UK express - Monday to Friday delivery.

See our Delivery & Returns for more information.

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  • Gluten free

    Gluten free

  • Vegan


  • Yeast free

    Yeast free

  • No added sugar

    No added sugar

  • Artificial colour free

    Artificial colour free

Key benefits

Friendly bacteria suitable for those with bloating

  • An easy, short-term option Designed to be taken over 7 consecutive days (1 sachet per day) 
  • Scientifically proven Passes through stomach acidity and reaches the gut
  • Quality, multi-strain formula Containing various high quality strains of friendly bacteria
  • Highly researched strains Such as L. acidophilus/helveticus Rosell-52, found to support digestive enzymes including lactase & α-glucosidase, involved in the breakdown of lactose in milk & starch
  • A more natural option Complements your natural gut bacteria, and free from artificial flavours often found in other food & drinks containing live cultures
  • Highly recommended From the UK’s most trusted & recommended brand of friendly bacteria supplements.

One Week Flat can be taken occasionally for 7 consecutive days once a month or on an ongoing basis.

Optibac Probiotics strains

  • Lactococcus lactis Rosell-1058
  • Lactobacillus casei Rosell-215
  • Lactobacillus acidophilus/helveticus Rosell-52
  • Bifidobacterium bifidum Rosell-71

Added nutrients

  • FOS fibres
See full ingredients list

General digestive


Complements gut bacteria

Customer reviews

4.2/5 (85 reviews)
  • At 61 years of age and a life time of bloating and looking 7 months pregnant most of he time I have tried practically everything on the market and diets and exercise regimes. I came across 7 days flat on yet another desperate web search to find the solution. Well I found it in 7 days flat. First 2 days I felt a bit dizzy ( may be unrelated), by day 4 I saw and felt a difference.. by day 7 the gas reduced to a large extent. Could button and zip trousers with ease. I stopped after 7 days and still felt good. I am travelling later in week and have started again. It is worth giving this product a chance.

    Caroline- 10th January 2023

  • This product is a total game changer. I’ve tried all the opti bac products but this one seemed to agree with me the most and I now take these daily. The opti bac team have been great with their customer care and have been committed to helping me find a product that works for me. Thank you!

    Lauren- 1st March 2022

  • Used to get so bloated whenever i had my period. I take a course once a month, starting a 2 or 3 days before my period is due

    Jessica O- 17th January 2022

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Help & advice

Speak to our team of experts (nutritionists, microbiologists and nutritional therapists) any time for free advice, with absolutely no obligation to buy.

Camilla Gray
Camilla Gray DipCNM Nutritional Therapist

Why choose us?

We are the UK's most trusted & recommended brand of friendly bacteria supplements.

† As determined in an independent survey of 1000 British women.

  • How to use

  • Ingredients

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  • Delivery & returns

  • How to use

    Recommended use

    Natural food supplement suitable for adults and children (from 4 years onwards) with the following recommendations:

    • Take 1 sachet daily for 7 consecutive days, preferably with breakfast.
    • Pour an inch of water into a tall glass, leaving plenty of room for swirling.
    • Shake the sachet before gently sprinkling the powder into the glass.
    • Vigorously swirl the water around in the glass making sure the powder is dissolved.

    We highly recommend you take One Week Flat for 7 consecutive days. Many consumers like to take this course once a month. However, it can be taken on an ongoing basis or as desired.


    • Store in a cool, dry place below 25°C and out of direct sunlight.


    Live cultures are not recommended for those with serious medical conditions e.g. those who are severely immunosuppressed, have pancreatitis, are in the ICU, have melaena, have a central venous catheter, infants with short bowel syndrome, or patients with open wounds following major surgery; unless under a doctor's care. Keep out of reach of children.

    Gut health supplements are not intended to prevent, treat or diagnose any medical conditions. If taking probiotic supplements for gut health, note that these should not be used as a substitute for a varied and balanced diet and a healthy lifestyle. If you are taking any medications or have a serious medical condition, consult a doctor before use. Optibac supplements will not cause dependency and may be used on an ongoing basis.

  • Ingredients


    Maltodextrin (natural source); Fructooligosaccharides (FOS 0.3g); Live cultures: Bifidobacterium bifidum Rosell-71, Lactobacillus casei Rosell-215, Lactococcus lactis Rosell-1058 and Lactobacillus acidophilus/helveticus Rosell-52

    Each sachet guarantees 5 billion live cultures + 0.3g FOS fibres.


    • Vegan
    • Vegetarian
    • Gluten free
    • Yeast free
    • No added sugar
    • Suitable during pregnancy
    • Suitable during breastfeeding
    • GMO free
    • Flavourless
    • Free from artificial flavourings, colourings and preservatives
    • No chemicals or parabens

    Following the taxonomic updates by a global team of scientists and published in April 2020, a reclassification has been advised for the L. casei species. The casei strain in the Optibac One Week Flat product is now also known as Lacticaseibacillus casei Rosell-215.

    Visit the Probiotics Learning Lab to find out more about friendly bacteria supplements and bloating.

    Format Sachet
    No. Live Cultures 5 billion
    Added Ingredients FOS Fibres
    Recommended Use 1 sachet daily
    Age Range Adult
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  • Delivery & returns

    UK Delivery

    Free UK Delivery over £40 
    Free standard UK delivery is automatically applied at the checkout when you spend £40.

    Standard 2nd class: £2.50
    Allow 4-10 working days (Monday - Friday) for delivery 

    1st class: £3.95
    Allow 1-3 working days (Monday - Friday) for delivery 

    Express Next Day (Tracked): £6.95 (Dispatching Friday 30th December)
    Order before 2pm for 1-2 working day delivery to most of the UK*. Orders placed on Friday will be delivered on Monday (next working day). Requires signature.

    Shipments will be dispatched via DHL or FedEx, the service will be selected depending on the delivery location.

    *Express delivery may exclude the Channel Islands, Herm Island, Isle of Man, Isle of Wight, Northern Irish postcodes BT18 & upwards, Sark, Scottish borders and offshore and a small number of remote mainland destinations as determined by our delivery courier. 

    Good to know

    • We'll send you an email to confirm once your parcel has been dispatched.
    • For delivery queries, please call us on +44 (0)1264 339 770 or email
    • Orders placed before 2pm are typically dispatched on the same working day.
    • Delivery within the UK and Northern Ireland has a fixed price, regardless of the size and weight of your order. 
    • Delivery times are estimates and not guaranteed unless otherwise stated.

    International Delivery

    We offer an excellent worldwide delivery service. For more details, please take a look at our delivery FAQ.


    If you have changed your mind, you can return goods, at your cost, unopened within 14 days for refund or exchange, this does not affect your statutory rights.

Customer Questions

All questions answered by probiotic experts Dr Kate Stephens PhD (Food and Microbial Sciences) BSc(Hons) Medical Biology and Kerry Beeson BSc (Nut. Med.) Nutritional Therapist

Initially it’s best to take Optibac One Week Flat daily for one week to complement your natural gut bacteria. After that, people take a week’s course every month, or whenever they feel they need it. Others prefer to take one sachet every day on an ongoing basis. All of these options are absolutely fine! See what suits you best.

With only 7.72 calories per sachet, and 0g of fat, it’s easy to include Optibac One Week Flat in your calorie-controlled diet. The carbohydrate content is mostly from natural FOS fibres which are indigestible with barely any calorific content.

Yes! One Week Flat is carefully formulated to have a slightly sweet, ‘neutral’ flavour which most people find pleasant to take. However, be reassured that the supplement contains no added flavourings, sugar, or sweeteners – the mild sweet taste comes from the natural Fructooligosaccharide (FOS) fibres.

One Week Flat is dairy and gluten-free, so is a perfect supplement for those with food-related bloating or lactose intolerance (1,2,3). This high-quality supplement contains four, highly-researched friendly bacteria strains combined with natural FOS fibres, which together help to complement the gut microbiome.

(1). Rampengan et al., (2010), ‘Comparison of efficacies between live and killed probiotics in children with lactose malabsorption’. Southeast Asian Journal of Tropical Medicine and Public Health 41: 474-481 (2). D. H. Juers, B. W. Matthews and R. E. Huber, “LacZ β-galactosidase: Structure and function of an enzyme of historical and molecular biological importance,” Protein Science, vol. 21, no. 12, pp. 1792-1807, 2012.# (3). Oak SJ, Jha R. The effects of probiotics in lactose intolerance: A systematic review. Crit Rev Food Sci Nutr. 2019;59(11):1675-1683. doi: 10.1080/10408398.2018.1425977. Epub 2018 Feb 9. PMID: 29425071.
Read More

Definitely! Friendly gut bacteria are not gender-specific. Optibac One Week Flat live cultures can be taken by everyone over the age of 4 years: women, men, trans and non-binary people too!

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