Is fibermaxxing (eating as much fibre as possible) healthy?
Eating more fibre is well supported as healthy for most people, but overdoing it causes gastrointestinal complaints and no additional benefit has been demonstrated. Aim for 25 to 29 grams per day through regular food intake.
People in Western countries structurally eat too little fibre, well below the recommended amounts. Eating more fibre is therefore worthwhile for most people. The only question is: how much is healthy, and what happens if you overdo it?
The strongest associations concern mortality and cardiovascular disease. People who eat more fibre die 23% less often from any cause, and 26% less often from cardiovascular disease. The risk of pancreatic cancer and diverticular disease is also demonstrably lower with a higher fibre intake. These are associations from large population studies, not proof that fibre is the direct cause, but the relationship is remarkably consistent for these outcomes. Fibres from nuts and seeds stand out in particular: people who eat a lot of them have a 43% lower risk of dying from cardiovascular disease. Insoluble fibres, such as those found in wholegrain products, appear slightly more effective than soluble fibres for reducing mortality. Both types count, but not all fibres are equal.
For the gut, the benefits are also well documented. Higher fibre intake is associated with better bowel function and a lower risk of colorectal cancer. If you want to concretely improve bowel function, you can try soluble fibres such as psyllium: 10 to 15 grams per day, for at least four weeks. For long-term protection against cancer and cardiovascular disease, the target is 25 to 29 grams per day through varied food intake, sustained over the long term. How you reach that amount matters less than actually getting close to it.
Now for the limits of 'maxxing'. Too much fibre in a short period of time causes stomach pain, bloating, flatulence and diarrhoea in many people. In rare cases, bowel obstruction has been reported. Increasing intake rapidly without drinking enough water raises that risk. Building up slowly and staying well hydrated limits the discomfort. There is no evidence that extreme fibre intake provides additional health benefits beyond the 25 to 29 grams per day that the research identifies as effective. Beyond that point, you do not know what you stand to gain, but you do know what you can lose in terms of comfort.
This answer draws on multiple review studies summarising tens to hundreds of participant studies, including two reviews that assess the overall body of evidence for quality. The associations concerning mortality and cardiovascular disease are consistently found across multiple independent large analyses and have been classified as strong. The associations concerning diabetes, body weight and the microbiome are less clear-cut and are based on smaller or mechanistic studies. All key findings come from population studies in which people were followed over time, with no demonstrated cause-and-effect relationship. The negative effects of excessive fibre intake are described in one review.
Is eating organic really healthier?
Eating organic probably does not give you better nutritional value, but it does lower your exposure to pesticide residues and to antibiotic-resistant bacteria through meat. For pregnant women and young children, that is the strongest concrete argument.
How much fibre do I need and why?
Aiming for 25 to 29 grams of fibre per day is well supported and delivers the greatest health benefit. Most people in Western countries fall well short of that, so eating more vegetables, legumes and wholegrain products is a smart step for almost everyone.
Is soy healthy, or not because of the phytoestrogens?
Soy is probably harmless and possibly beneficial for most healthy adults, but caution is advised for children with thyroid problems. Anyone who eats a lot of soy and has doubts is best off discussing this briefly with a doctor or dietitian.
Are smoothies and fresh juice just as healthy as whole fruit?
Whole fruit beats fruit juice: more fibre, greater satiety and fewer free sugars. Smoothies fall somewhere in between, but are not equivalent to whole fruit either.
What does eating fibre do to your gut microbiome and your long-term health?
Fibre demonstrably feeds your gut bacteria, improves stool consistency and protects the gut wall. But how your microbiome and immune system respond varies considerably from person to person.
Does eating more fibre help against high blood sugar?
Water-soluble fibre from legumes, vegetables and fruit probably helps lower high blood sugar, but the overall composition of the meal also plays a role. For type 2 diabetes and gestational diabetes, consulting a doctor is always necessary.