In July this year I wrote about the link between the bacteria in the digestive system and obesity.  The human adult gut contains up to 100 trillion microbial organisms and it certainly seems sensible to ensure that these are mainly made up of ‘friendly’ good bacteria.  The type of bacteria in the digestive system seems to have an effect on the entire body and not just the health of the gut.

A recent study (1) has found that prebiotic supplementation was associated with reduced appetite sensation after a meal.  Prebiotics act as food for the good ‘friendly’ bacteria in the digestive system and previous studies (2) suggest that prebiotics in the diet may reduce our energy and food intake, increase satiety, reduce hunger and appetite and reduce total daily calorie intakes.  Prebiotics may also have positive effects on blood sugar balance in the body which can also impact appetite.  This recent research (1) was set up to see whether prebiotic supplements affected the hormones associated with satiety.  The study was very small but well designed and provided interesting results.  Prebiotic treatment was associated with a three fold reduction in hunger rates and an increase in hormones which are associated with feelings of satiety/fullness. 

In past blog posts I have mentioned many nutritional ways that can help to keep us feeling satisfied after a meal and may hence prevent over eating, or even cravings (which are often related to blood sugar imbalance).

Again, I would like to stress that obesity is a complex disease involving many factors with no miracle cure and no easy solutions - I am not about to disillusion anyone by inferring that bacterial balance is a major factor and probiotic or prebiotic supplements are the cure.  However, gut bacteria may well be having some kind of impact on the development of excess body weight in some people.  What we eat does affect the composition of the microorganisms that are present in our digestive systems and in turn these microorganisms can have an effect on the health of our body.  A review paper (2) stated that “probiotic and prebiotic supplements may be useful in order to positively change the gut bacterial balance and help prevent and treat overweight but that these manipulations should clearly not be viewed as a substitute for a healthy diet and exercise”.

Further conclusive evidence needed, however prebiotics (such as FOS) and probiotics do seem to positively change the composition of bacteria in our digestive systems and affect overall health.  Supplements are readily available but should not be seem as a quick-weight loss fix.  A healthy diet and lifestyle is of paramount importance for weight control and overweight prevention and treatment.

Another factor to mention here is fibre (since prebiotics are a form of fibre), a high fibre diet can also help with feelings of fullness and therefore prevention against over-eating.  A recent study (3) in young people (aged 11-17) at high risk of obesity found that an increase in total dietary fibre intake was associated with decreases in fat tissue.  A decrease in fibre was associated with significant increases in fat tissue, this was noted even if the decrease in fibre was small (about 3g).  The authors of the study conclude that “Small reductions in dietary fiber intake over 1–2 y can have profound effects on increasing visceral adiposity [fat mass]”. 

A diet that is high in fibre has been linked to numerous health benefits in most areas of the body from the: heart, where it seems to have positive effects on blood pressure and risk of heart disease; digestive system where it seems to be useful to sufferers of irritable bowel syndrome (IBS), constipation and diverticulitis and the immune system where there seems to be a link with reduced risk of cancer.  A high fibre diet also appears to be very useful in blood sugar control and also appetite control as it gives us the feeling of fullness and helps to control satiety.  The recommended daily intake for fibre in the UK is currently set at 18g/d, however for optimal health many experts regard at least 25g per day as necessary.  In the UK our average intake is low at only 12g/d.  Foods that are naturally high in fibre are also a really important part of a healthy diet e.g. vegetables, fruits, beans/pulses, nuts/seeds and wholegrains.

(1)Cani PD et al.  2009.  Gut microbiota fermentation of prebiotics increases satietogenic and incretin gut peptide production with consequences for appetite sensation and glucose response after a meal.  Am J Clin Nutr.  90:1236-1243
(2) DoBaise JK et al.  2008.  Gut microbiota and its possible relationship with obesity.  Mayo Clinical Processings.  83:460-469
(3) Davis JN et al.  2009.   Inverse relation between dietary fiber intake and visceral adiposity in overweight Latino youth.  Am J Clin Nutr.  90:1160-1166
Written by Ani Kowal

In order to successfully lose and maintain a healthy weight it is necessary to eat nutritious foods that satisfy appetite.  Foods that release sugar slowly into the bloodstream, i.e. foods that have a low glycaemic index (GI) help us to keep appetite on an even keel and prevent cravings.  Including protein with each meal also helps since protein tends to help satisfy hunger more than carbohydrate or fat.  If we don't feel as hungry it is often easier to control our food intake.

Can fish oils help satisfy our appetites?
A recent study (1) looked at long chain omega 3 fatty acids, fish oils, to determine whether intake of these fats affects appetite when given to individuals following a low calorie diet.  These long chain fats (EPA and DHA) are found in oily fish such as salmon, trout, sardines and mackerel.  The study involved individuals aged around 31 years who were overweight (with an average BMI of 28).  Their appetite was explored during the last 2 weeks of an 8 week energy-restricted, balanced diet.  Half of the participants had a low amount of long chain omega 3 fatty acids as part of their diet and half had a high amount (over 1300mg per day).  Blood from the participants was measured to detect any changes in fatty acid levels and a validated assessment was used to measure hunger sensations directly after a 2 hour test meal.  As expected, the omega 3 content in blood cell membranes was lower in the low omega 3 intake group. The validated assessment revealed lower hunger sensations in the high omega 3 fatty acid group immediately after the test dinner and 2 hours later i.e. their appetites appeared to be satisfied and they felt fuller even 2 hours after the meal. 

The authors of the study conclude that long chain omega 3 fatty acid intake regulates after-eating (postprandial) satiety in overweight and obese volunteers during weight loss. Further research is needed to investigate the effects of omega 3 fatty acids in appetite control and weight loss maintenance.

There may be many reasons why omega 3 fatty acids help to prevent hunger and increase feelings of satiety after a meal.  One reason could be that omega 3 fats help to keep our blood sugar levels stable by affecting the way that our bodies deal with the hormone insulin (vitally needed for blood sugar control).  A recent study (2) found that long chain omega 3 fatty acids do indeed have positive effects on insulin control in young overweight individuals on a low calorie diet.

Omega 3 fatty acids are vital for our health and wellbeing.  Eating oily fish at least twice a week will help to keep levels in our body high.  For those who do not regularly eat oily fish then an omega 3 fatty acid supplement which provides around 250-350mg DHA and 250-350mg EPA daily may be beneficial.  Vegetarians and vegans can find short chain omega 3 fatty acids within flaxseeds and walnuts and may consider a flaxseed oil supplement providing 500-1000mg alpha linolenic acid daily.  Some long chain vegetarian omega 3 supplements are now becoming available, these are produced from algae.  Phytoplankton (microscopic marine plants) supplements also contain some EPA and DHA.

Oily fish may be beneficial in reducing appetite levels since it is a low GI food and very rich in protein, both factors which seem to have appetite-sating effects.  In addition to this there is evidence for omega 3 fatty acids being beneficial to our mood and in helping people who deal with depression, perhaps this mood boosting effect helps with self-esteem and hence may be a useful tool in curbing comfort eating?  Studies have not yet been done in this area but it seems like a plausible idea.

Why opt for low GI?

GI stands for Glycaemic Index.  Many supermarkets have now started to label low GI foods, but why is GI important to consider?  GI is a system of classification, or ranking, that is given to carbohydrate foods depending on how they affect our bodily blood sugar levels.  A low GI food or meal takes a longer time to release sugar into the bloodstream.  This means that insulin, the hormone responsible for blood sugar control is released in smaller amounts which helps prevent blood sugar fluctuations and consequent cravings and dips in energy levels.  A high GI food or meal releases sugar very quickly into the bloodstream, in response to this our bodies produce huge quantities of insulin which quickly remove the sugar from the bloodstream, often this leaves us feeling tired and lethargic and can cause cravings for more sugar or carbohydrate – leading to another surge in blood sugar levels and the start of a vicious cycle of insulin release and consequent cravings.

High GI foods include white bread, croissants and cornflakes and most processed or refined carbohydrates.  Low GI foods include most vegetables and fruits, most unrefined wholegrains and foods containing little carbohydrate such as meat, fish, eggs etc.

However, GI does not only affect insulin levels, it also seems to work to specifically reduce appetite.  A new study (3) presented at the annual Society for Endocrinology BES meeting this year has found that eating a meal with a low GI increases the production of a specific gut hormone called glucagon-like peptide 1 (GLP-1).  This hormone is known to help suppress our appetite and helps us to feel full after a meal. This is the first study to provide clues as to how a low GI meal produces satiety after a meal.  The study was small and results need to be verified in larger trials but it is indeed an exciting development. 

Previously I have written about eating to control blood sugar levels and how work stress can affect appetite  Reading these posts may provide you with a few useful ideas on how to keep appetite on an even keel throughout the day.  Essentially a healthy diet that includes an abundant variety of vegetables and fruits, healthy fats from nuts/seeds and oily fish, protein from unprocessed meats, fish, beans and pulses and minimal amounts of refined and processed carbohydrates will go far in boosting health and reducing waistlines.  Eating ‘real food’ satisfies taste buds, provides essential nutrients and keeps us healthy. 

(1)Parra D, et al.  2008.  A diet rich in long chain omega-3 fatty acids modulates satiety in overweight and obese volunteers during weight loss. Appetite.   Jun 14; [Epub ahead of print]
(2)Ramel A et al.  2008. Beneficial effects of long-chain n-3 fatty acids included in an energy-restricted diet on insulin resistance in overweight and obese European young adults. Diabetologia.  51(7):1261-8.
(3)Norouzy A et al.  2009.  Effect of single high vs low glycemic index (GI) meal on gut hormones.  Presented at Society for Endocrinology BES 2009, Harrogate,UK.Endocrine abstracts 19 OC17

The Society for Endocrinology is Britain's national organisation promoting endocrinology and hormone awareness.  The Society for Endocrinology BES 2009 is Britain's biggest scientific meeting on hormones, took place at the Harrogate International Centre, Harrogate, from 16-19 March 2009.

Written by Ani Kowal