“Universal dietary recommendations may have limited utility.” 

Healthcare professionals who have attempted to help patients lose weight—or who have struggled with weight loss themselves—can confirm that that is quite an understatement. More starkly one need only to do some people-watching in public places to be faced with the simple reality that one-size-fits-all nutritional guidelines have been an abysmal failure. While some people are successful on a low-fat low-calorie diet others seem to gain weight by just looking at a cupcake. Some people thrive on low-carbohydrate diets; others feel their best on diets that exclude animal foods. When it comes to optimizing nutrition for weight loss and overall health healthcare practitioners working “in the trenches” of a clinical setting have long known something the ivory tower folks are just starting to acknowledge: different people do best on different diets.

Culinary history fossil evidence and the anthropological record indicate that the human species is fantastically adaptable to a wide range of climates topography and food sources. From Arctic peoples’ high-fat seafood diet to Pacific Islander diets higher in fruit and starchy tubers it’s clear that “healthy diets” can have very different macronutrient ratios. The key thing to note however is that even though humans can thrive on a wide variety of diets that doesn’t mean that all humans can thrive on all diets. 

This really shouldn’t surprise anyone. Considering the genetic differences in methylation pathways detoxification capacity and differing levels of insulin sensitivity and carbohydrate tolerance it’s actually fairly logical that individuals would feel their best and attain their optimum health on different diets. This last point—variations in insulin sensitivity and carbohydrate tolerance—was the focus of a recent study that revealed in no uncertain terms just how misguided blanket nutritional recommendations are.

The study conducted by the Weizmann Institute of Science in Israel followed a cohort of 800 people over the course of week and continuously monitored their glucose levels in response to a total of 46898 meals. The results showed that the very same foods led to wildly different glycemic responses among individuals. This calls into serious question the concepts of glycemic index and glycemic load. It is now understood that these are not fixed values. How quickly and how high someone’s blood glucose rises after consuming a particular food is not solely the result of something inherent to the food itself but rather how an individual’s unique biochemistry and genetic makeup are influenced by the carbohydrate content and makeup of that food. One person’s low-glycemic high-fiber cereal could be another’s white bread with grape jelly.

With regard to glycemic responses after consuming the same foods study author Eran Segal noted “There are profound differences between individuals—in some cases individuals have opposite response to one another and this is really a big hole in the literature.” Again an understatement. Segal also noted “After seeing this data I think about the possibility that maybe we’re really conceptually wrong in our thinking about the obesity and diabetes epidemic. The intuition of people is that we know how to treat these conditions and it’s just that people are not listening and are eating out of control--but maybe people are actually compliant but in many cases we were giving them wrong advice.” (Emphasis added.) 

These observations are welcome news to patients who have spent years—sometimes decades—doing what they were led to believe were “all the right things” yet still struggled with weight loss blood sugar management blood lipids and more. It also explains why people have such different results upon following the same diet.

Somewhat similar findings were revealed by the A TO Z Weight Loss Study which compared weight loss in premenopausal women who followed the Atkins LEARN Ornish or Zone diet. All of these diets led to weight loss in at least some of the participants with the Atkins diet (low-carb high-fat) coming out on top. Moreover after twelve months of following these diets (in a free-living setting) secondary outcomes—which included lipid profile body fat percentage waist-hip ratio fasting insulin and glucose levels and blood pressure—among the Atkins dieters were comparable to or better than the other groups. When the data were analyzed further it was revealed that the subjects who did best on the low-carb diet were those who were insulin resistant. Individuals with greater insulin sensitivity and stronger carbohydrate tolerance seem to fare well on lower fat diets but the across-the-board guidance for everyone to follow a low-fat diet has clearly been disastrous for millions of people.

Based on the data collected in the Israeli study researchers created an algorithm that integrates blood parameters dietary habits anthropometrics physical activity and gut microbiota in order to predict personalized postprandial glycemic response to meals. The algorithm was validated in a subsequent 100-person cohort followed by a randomized controlled dietary intervention based on the algorithm. The results showed significantly lower postprandial glucose responses and consistent alterations to the gut microbiota. This is the cutting-edge of personalized nutrition wherein specific foods and food combinations could be recommended or advised against based on an individual’s biochemical parameters and health goals.