From The Times
London, UK
11 March, 2017
Which carbs are really making you fat?
Why does the same diet work for some people and not for others? A groundbreaking new book by American scientist Robb Wolf claims that everyone has their own unique response to specific carbohydrates
Ask most people about the best way to lose weight and they will say that, although calories matter, the modern route to a lean physique is managing your carb intake. By avoiding “bad” carbohydrates such as sugary foods, pasta and bread, and consuming “good” carbohydrates such as whole grains and non-starchy vegetables, you avoid the blood-sugar spikes that make the body store fat.
However, we also know that low-carb, high-protein diets do not work in the same way for everyone. Some people shed pounds quickly after giving up carbohydrates, but others can’t seem to budge the needle on the scale very far. Those frustrated dieters often return to their old eating habits, and sooner or later the whole painful weight-loss process begins again.
Now a growing body of evidence points to the imminent demise of the one-size-fits-all approach to diets.
Researchers have found that carbs trigger different blood-sugar responses in different people and this is likely to be one of the reasons why so many diets fail.
A new book, Wired To Eat, by Robb Wolf, a research biochemist turned health consultant and the author of the New York Times bestseller The Paleo Solution, says that personal nutrition — tailored eating habits related to an individual’s biology — may be the key to permanent weight loss and better health.
We can rewire our appetite to determine the optimal foods for our diet and metabolism, Wolf claims, by finding out which types of carbs we tolerate. In doing so we can set ourselves up for a slimmer, more vigorous future.
“You can learn the amounts and types of carbs you can eat while staying lean and healthy. No more guessing which foods are right for you,” says Wolf.
In a 2015 study on personal nutrition at the Weizmann Institute in Israel, 800 people were screened to determine the composition of their gut microbiomes — the microbe population in the intestine. Gut bacteria play an important role in digestion, ensuring that we get the nutrients we need, and influence our health and susceptibility to disease.
The participants had blood tests that screened for cholesterol levels, blood glucose and inflammatory markers, and completed lifestyle questionnaires.
Each was given equal amounts of specific carbohydrates, and their blood glucose levels were monitored.
The results showed that glycaemic response — changes in blood sugar after consuming carbohydrates — differs widely from person to person, and is highly influenced by genetic factors, exercise, body-fat levels and the contents of the gut.
One participant had a pronounced increase in blood sugar after eating a banana, but had a good blood-glucose response after eating a sugar-laden biscuit, for example, while the opposite response was recorded for another participant.
One woman was eating a healthy diet of vegetables, but her blood sugar soared when she ate tomatoes. “Technically, tomatoes are carbs, but you would have to eat a truckload of them to get significant amounts of carbohydrate — yet this lady had blood-sugar spikes after eating them,” Wolf noted.
Many of the results were so counterintuitive that even the researchers were surprised. Some of the volunteers did not register blood-sugar spikes in response to ice cream, but had high blood sugar after eating white rice.
“There was massive variation from person to person in how they reacted to various foods,” Wolf says. Taking this information, the researchers created an algorithm to check whether the findings held up with a second group of 100 participants. The algorithm integrated blood tests, dietary habits, body size, physical activity and gut microbiomes of the sample group, and accurately predicted personalised post-meal highs and lows in blood-sugar response. In his book, Wolf calls the findings “one of the most important research projects in the past 50 years”.
He says: “Some people avoid bread, rice, beans and most other foods that contain a significant amount of carbohydrate and they lose weight. But they are often left wondering if they will have to eat this way for ever. Now we can zero in on problematic foods quickly and find the amounts and types of foods you do best with.”
More research needs to be done to discover exactly why people react so differently, he acknowledged. “But it is likely to be the interaction between an individual’s genetics and their gut micro-biome.”
In the final stage of the study researchers found that eating a diet that kept blood-sugar levels stable appeared to “rehabilitate” the gut by reducing inflammation and re-establishing healthy gut bacteria.
In Wired To Eat, Wolf suggests that people pinpoint how much latitude they have in what they can eat with a seven-day carb test, measuring blood-glucose response to specific carbohydrates.
Why should we be concerned about spikes in our blood-glucose levels and what is an ideal blood-glucose level? “It’s been observed over time that significant changes in blood-glucose levels tend to lead to more overall food consumption,” Wolf says. “It appears the brain does not ‘like’ large swings in blood sugar. This may be why we become hungry after consuming large quantities of carbohydrates.”
Blood-sugar spikes also encourage the body to store fat and are highly correlated with increased rates of many diseases, including diabetes, various cancers and neurodegenerative diseases such as Parkinson’s and Alzheimer’s, says Wolf.
Blood glucose is measured in millimoles of glucose per litre (mmol/l) and levels fluctuate throughout the day. Ideally, Wolf says, blood glucose should be between 5 and 6.4mmol/l two hours after eating.
Wolf himself had a wildly different personal response to white rice and to lentils. After eating the rice, he says, his blood glucose was 8.6mmol/l. “This is effectively diabetic blood-sugar levels.”
For the lentils, his blood sugar was 5.2mmol/l. As a result, Wolf says, lentils and other pulses are a staple of his diet because he knows they help to keep his blood-sugar level stable. He limits rice to an occasional small helping.
Some people may find the notion of tracking blood sugar for a week to be a bit over the top, Wolf accepts. “But what we now know is there is huge variability from person to person in how one responds to various meals, and without testing we are just guessing. Given how much better people will look, feel and perform if they get this ‘right’, a week is a small ask in the bigger picture.”
Ideally, he says, this testing should be done after a dietary reset, avoiding processed food and dairy products, sticking to meat, fish, nuts, leafy greens, vegetables and seeds. Essentially, this is a “paleo” diet and Wolf recommends doing it for 30 days before testing your responses to different carbs.
“A reset will help to shine a light on your regular eating habits, so I would strongly recommend it,” he says.
Wired to Eat: How to Rewire Your Appetite and Lose Weight for Good by Robb Wolf is published on March 21.
Try the seven-day carb test
With this easy test, discover which carbohydrates are best for you and which to avoid. Then you can create a personal nutrition blueprint that will help you to stay slim and healthy.
First you will need a blood-glucose monitor, the kind that people with diabetes use, which you can buy in a chemist for about £10. With the basic versions you prick a finger to extract a drop of blood and take a reading with the device. There are higher-tech versions that are worn like a temporary tattoo and communicate with your smartphone.
Over the next seven days you will eat a different type of carbohydrate at the same time each morning and measure the blood-glucose response two hours later. This gives you an idea of which carbohydrates your body processes most effectively.
Pick seven carbohydrates that you eat often and have a different one for breakfast each day — don’t have any other food. (If there are only five carbohydrates that you eat regularly you can limit the test to five days.
For example:
Day one
1¼ cups cooked pasta (200g)
Day two
Three slices bread (120g)
Day three
Two cups oats made with water (485g)
Day four
1½ baked potatoes (250g)
Day five
Two sweet potatoes (290g)
Day six
One cup cooked white rice (180g)
Day seven
Two thirds of a tin of chickpeas (255g)
You can substitute any of your “favourite” carbs for the above. To find out how much to eat for your carb-only breakfast, check its nutritional value — you need 50g of “effective” carbohydrate of your chosen food (total amount of carbohydrate minus the amount of fibre). No food is pure carbohydrate so, to calculate how much to eat for the test, check the label on packaged food for the carbohydrate per 100g — for everything else there’s Google. For example, quinoa has 30g of effective carbohydrate per 100g, so you would need to eat 165g of quinoa for the test to make sure you were getting 50g of effective carbohydrates.
If you want black coffee, tea or water with your test meal, that’s fine, as long as you do the same with each meal to keep the readings accurate. Apart from this, eat only the carbohydrate you are testing. You can do the test at other times, but breakfast is best.
Track your blood-glucose response two hours after your meal using your monitor. If the reading is between 4.4–6.4 mmol/l, you have a normal reaction. If it is higher then this food could be one to avoid. With a high reading it’s worth retesting on a different day.
“Properly managing our blood sugar is important for health, but even if we just want to look and feel better, and lose extra weight, it is helpful to get our blood sugar ‘right’,” Wolf says. “Avoiding the problems of high and low blood sugars help people to eat the right amount of food and avoid cravings.”
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