The ketogenic diet, popularly known as keto Diet has its advantages. However, most of the studies or observations were with those patients who did not have bariatric surgery or any other major change in the gastrointestinal tract. It remains a concern whether the Keto diet should be advised after bariatric surgery. There is no data at present to recommend keto diet after bariatric surgery.
Here are some concerns which come to my mind:
Bariatric surgery does induce volume restriction and the principal is to maintain that restriction for a longer period. It may not be easy to achieve the composition like the keto diet, for example, 70 per cent calories from fat, without compromising on the necessary elements like protein, fibre and minerals. At the same time, absorption of those calories is not certain in bypass procedures which may defy the mechanism of the diet. On the other hand, in some individuals or after procedures like sleeve gastrectomy or at times even bypass, it is likely that the total calories may even exceed than the usual bariatric norms.
The basic mechanism of the keto diet is the preferential use of fat as energy by inducing ketosis. There is no evidence to know whether this state of ketosis can be induced in the same manner after bariatric surgery, as if in a normal individual. The change in hormones after bariatric surgery and subsequent change in metabolism induces weight loss, rather fat loss.
Even though bypass procedures have fat malabsorption, one does not know whether we should offer this challenge of excess fat in these patients. It may induce rapid transit, frequency of stools, loose motions and malodourous stools in some procedures. It is not known whether dumping would be frequent and whether frequent dumping would be favourable. This different phenomenon may define a different ‘keto flu’ like syndrome in these patients after keto diet.
There would certainly a change in gut microbiota induced by a keto-type diet rich in fat and low in fibre. Whether it would lead to adaptation for better fat absorption is still not known. If it does, it may compromise the result of the procedure over the long term, especially with the question whether the keto-type of diet would be sustainable over the long term. In my experience, a few of the patients who attempted keto diet, succeeded in losing weight for a short period and eventually all 32 of them became candidates for revision in the next two to three years.
It appears that Keto-type of diet after bariatric surgery will aggravate protein, mineral and vitamin deficiency. Guidelines for these supplements may need to be modified while the individual is on a keto diet and will need further studies.
Keto diet may have to be modified, (if at all it needs to be attempted in a patient after bariatric surgery), studied with reference to efficacy, absorption, ketone levels, deficiencies, hormonal changes, impact on NASH, etc. Studies with longer follow up are needed before recommending it to a patient after bariatric surgery.
The keto diet does not work well after bariatric surgery for the following reasons:
- The high-fat content of the keto diet (70% of calories) does not allow for the consumption of adequate protein or carbohydrates.
- A high-fat diet may lead to fatty diarrhoea (steatorrhea) and reduced absorption of nutrients because food tends to travel faster through the intestinal tract after bariatric surgery. There is a risk for nutritional deficiencies after bariatric surgery; severely limiting specific food groups (whole grains, fruits, and many vegetables) only increases the chance that deficiencies will occur.
- Fat contains 9 calories per gram, while carbohydrates and protein contain 4 calories per gram—making fat a very concentrated source of calories. It is very easy to exceed calorie needs when consuming a high fat, low carb diet. Calorie intake 1 year or longer after bariatric surgery typically ranges from 800–1100 for women and 1000-1500 for men per day.
- The keto diet is low in fibre. This increases the risk of constipation, which can be a concern after weight loss surgery. Fibre may also reduce the risk of developing various conditions, including heart disease, diabetes, and diverticular disease.
Although the keto diet does show some short-term promising results for weight loss, it is not a good diet strategy after bariatric surgery. A lifestyle that supports a healthy weight after bariatric surgery is something that can be followed life-long, with protein at the centre of the diet. The keto diet with its extremely high-fat content, very low carb content, exclusion of grains and fruit, and low fibre content are potential concerns for overall health. This is even more of a concern after bariatric surgery when portions are limited and nutritional deficiencies are a risk.